Well that's definitely one problem with Sakurai, he thinks that would be good enough. Sakurai admits that he doesn't look at how fans react or really try to understand how fans thinks. So in his mind people were going to be completely fine with there character not being playable when they see that the spirit of their favorite character was "Legendary," like it's Sakurai's way of saying "We got you. We love these characters just like you do. They're important." when in reality it just doesn't do anything at all for the fans. And then there's Mii Costumes where Sakurai believes that they are like the best thing ever and that people are fully convince that they're playing as the character they always wanted. In his mind people cheered for the Rex Mii Costume being revealed. And he also believes that Assist Trophies are super hype announcement that don't disappoint anyone except for the fact that 9 times out of 10 the reaction to a favorite character being an Assist Trophy went like "NO!!!! WHY WHY WHY?!?!?" I'm pretty positive that he sat down with marketing and they all agreed that they would hold the Shadow Assist Trophy back until the November Direct so people would think "Is Shadow coming back? I'm getting worried." only for them to bust the roof of with his reveal and get so much praise.
Sakurai, while being great at making characters and listening to certain fan feedback, is really out of touch with the community. Which is why we keep getting stupid things like that Rathalos screenshot that look like a one for one recreation of the Golden Sun final boss fight, because Sakurai thinks people were going to love the look not that Isaac might've been hinted at. Thank God Banjo got after they showed that green witch in the custom stage builder reveal, there would've been a blood bath. Sakurai honestly thinks that doing this "meet you half way" style would please people when honestly it doesn't. No one cares about playing pretend with Mii Costume and people would rather the character not show up as an Assist Trophy if they weren't considered. For me Sakurai should either go all the way with the character or don't do it at all because as a customer who buy these games I'm not changing my perspective just to force myself to be happy because Sakurai decided that this course of action was for the best. He needs to get with the fans and understand them better. You can't please everyone, but you can do a lot better job at it if you know how they think.
You've been through this several times and people have disagreed with you for a lot of reasons. If you genuinely want to see what fans think of an Assist Trophy, go into the Isaac thread and ask them. Without his assist trophy, Golden Sun gets only Spirits, which is an objectively worse reality than the one we have now for most people, myself included.
I also call bull**** on the malicious intent of Sakurai. There's a ton of content to show off between reveal and release, and every single Direct had the job of deconfirming some characters through Assist Trophy reveals. If he had shown off Shadow early on, then he might have just been swapped with Waluigi who didn't show up til the end and caused a different outcry. At best he could have shown off all the Assist Trophies at the very beginning... but that offers him no tangible benefit and wouldn't solve a damn thing since some fans will just continue to complain, so I don't blame him for showing off what is objectively a pretty substantial feature of the game (I know you downright hate them, but they are a substantial part of the game like it or not).
And to address all of the supposed "Hints." The Smash fan base is rabid and sometimes downright paranoid when it comes to everything in existence acting as a hint or the basis for a theory. Of all the things Sakurai should be spending his time on, checking to make sure his every single piece of information and little screen shot or trailer inclusion isn't inspiring another dumb as hell chairs moment ain't one of them. Fans have got to take repsonsibility for their own hype in situations including stuff like a generic Green witch and a bunch of sword characters fighting Rathalos. That's not on Sakurai and it shouldn't be to begin with, we're the people who make those theories and jumps. We better damn well own that 100% personally manufactured hype and not complain when a long shot theory or "reference" doesn't amount to anything.
I'd also say that the thing with characters like Isaac, Geno, and Banjo is that they're characters people want a revival for, and I honestly wonder whether Nintendo or Sakurai are aware of what their inclusions would (and in the case of B-K, do) mean. Either the character will make a glorious return started by Smash, or they will have one last, big hurrah via Smash. As a Banjo fan, him and Kazooie getting in means the world to me. I'm so, so happy that they're finally home, and as much as I ADORE K. Rool, they're gonna usurp his spot as my main. They mean so much to me, and they haven't been around in years.
Isaac is the same way for a lot of people, even having a dead franchise and everything (even moreso than B-K, because at least they still get merch and acknowledgment). Geno is a character that hasn't been used in even longer, over 20 freaking years (not counting the SSS cameo). Some people have been waiting decades for him, much as I've waited exactly two decades to see B-K get in Smash. I've been a Geno fan for a shorter amount of time, and it's already been incredibly rough. I can't imagine how terrible his very, very long-time fans feel to get shafted so often.
When it comes to a character like, say, Waluigi or Shadow, their lack of inclusion is sad, but at least we can look forward to their future appearances in other games. The aforementioned three don't have that (or at least Isaac and Geno don't, because B-K has Smash inclusion now, something to look forward to!). That's what makes those situations that much more painful. At least Isaac is first party, too (well, second party, but just about as easy to just use), but Geno? He's in SE's hands. That makes a revival so much harder outside of Smash. Smash is so make-or-break for Geno that it hurts.
When it comes to characters like these, we just want to see them come back. If they can't be in Smash, something else outside of it would be fine. We don't ask for much. We just... want to see them again. Thankfully, I'm not an Isaac fan (because god, that would be suffering), but as a Geno fan, it's rough when we're basically the ultimate afterthought. We get a few SMRPG nods and a PNG in terms of new material this game... and that's it. I honestly can't fathom how Nintendo thinks people will be ecstatic about that. Understanding that it's unfortunate compensation, fine, but according to Sabi, they were so blown away by how bad Isaac's AT was received. They think people will be happy with that, and, well... that's clearly not the case.
I don't think we should place an expectation on Smash to act as a revival tool. That feels like a teritiary objective at best and Sakurai has just chosen characters because he or the fans like them (we thankfully have both on our side at least). That's a big burden on the roster I think and starts pushing into the territories of arbitrarily labeling which characters have "greater reason" to be in Smash over others. Like, I'm sure Sakurai realizes the importance to the fans of bringing any character into Smash and these characters contribute to the game, but you can really argue that of any character. There's no reason to value that "won't appear again" status over other considerations for inclusion in Smash, and in fact we've seen that hurt more characters than help them. I'd say it's very hard to assign much value to that label unless there's a serious fan movement also behind that character. That's the best we can do for these characters is create fan involvement and rally behind them, but some are just always going to have incredibly uphill battles for inclusion as a playable fighter.
There's generally a reason why we haven't seen these characters make more appearances since going more dormant. Banjo Kazooie got the most screwed arguably with his franchise just sort of being left to die because the people behind their games made a completely different game and called it Banjo Kazooie, and then abandoned him because they didn't want to work on old IPs. Geno's next, but he's more a victim of circumstance than malice. Square Enix and Nintendo broke up pretty much right after Super Mario RPG released, and as a sort of joint character who belonged to Square Enix he just didn't have a place in any games. If it makes you feel any better though, he's really only had a chance of coming back in the past decade, so we can at least not attribute it as much to any sort of active disinterest.
Isaac and Golden Sun had their chance and they blew it honestly. Nintendo made a big deal about making a new game when they revealed Dark Dawn in 2009, and then when it released, it sold absolutely dreadfully. For as much as fans would like to make a big deal of the series, they didn't turn out to actually support it when the sequel was released, and while it was a step down in quality from the original games, it was their chance to prove something to Nintendo. 2010 would have been a perfect time to consider Golden Sun for Smash seeing as how the project plan for 4 focused on 2009-2012, Dark Dawn's abysmal sales just meant that they absolutely missed their best chance for GS in Smash. Those sales might also speak to the fan base being smaller than the Smash bubble assumes.
I don't think Nintendo expects us as fans to be ecstatic about things like a Geno spirit, but I do think they expect a little bit of appreciation for remembering to include a character or make references to games that they clearly aren't investing in for the future. I mean, how many series have been resigned to a lesser fate than either Geno or Golden Sun? Advance Wars lost their assist trophy, as did Sin and Punishment. Rhythm Heaven has never managed to get anything beyond Stickers, Trophies, and Spirits. Hell,
Golden Sun has as much music as Final Fantasy in Ultimate. It may not be entirely what the most hardcore fan bases want for these characters, but it's something that does require work and as a producer/developer, you have so many people to please and you're never going to be able to please all of them, so you make compromises to give them something.
