It's worth noting that last time they tried to make a campaign was SSE. It took up too much of Brawl's development time and caused multiple game delays while also making it severely hard to balance the core game.
Smash is going to always have a lot of characters. That's the core part of what makes Smash, well, Smash. It's a character-driven game.
A full campaign is next to impossible unless we lose at least around half the characters, and they couldn't even include the full 35 in Brawl either. Not just due to delays, but a lot of clones(well, semi-clones) were added too late. It's too difficult to make a good one at this point and include the entire playable roster. That's why they're more like events or Melee's Adventure Mode, simplistic ones that are able to be worthwhile for all the characters in the game. Everyone is able to be incorporated in a useful manner. Cutscenes also take a lot to develop as is. They're a huge time sink. They were toned down heavily since Brrawl, which to make it even more clear, took up 70% of the full development time. Let's note that 7 characters didn't make the cut(though we don't know what Pra_Mai is exactly) because of they had no time to do so. Adventure Mode is a fun thing, but characters should come first before that.
For Ultimate, I do find it kind of boring at this point. It has a great roster, but little to do. Events are barely there, and Spirits become tedious since they're fairly difficult. Spirits are easily better than Trophies outside of lacking a description. Trophies require a full model and take longer to make sure it animations correctly when simply moved around. We've had some errors on models before, so it's not like this issue doesn't come up. They also take way longer to add than a picture, and descriptions need to be translated to multiple languages as is, an even bigger time sink. I miss trophies and descriptions, but I do think they did a good job at returning custom equipment and reinventing Trophies with Spirits overall. My only disappointment is that some of the DLC ones aren't including a lot of neat characters.
That said, we've gotten most modes back from other games. I get why Board The Platforms isn't coming back. It more or less has similarities to Adventure Mode in some way(well, the normal ones), and Race to the Finish often has the same elements of it so it's a bit redundant. The lack of any kind of Target Test(I'll gladly take Angry Birds style back, which I also liked incidentally, if it means having some kind of Target Test again). I prefer the idea of stylized ones, but Brawl handled it rather poorly. Having 5 levels isn't that bad, but it doesn't really translate well for a ton of characters. Level 5 can be a serious pain for some to even do. It also means you need to do far more Target Tests than if it was one per character(or even one per franchise, but every character would need to do it at least once). They aren't counting transformations from what I remember, but you still need to do 175 levels overall. That sounds pretty tedious. I could slightly forgive this annoyance if Brawl's Classic wasn't painfully long, extremely repetitive with barely any variety much of the time, and had only two mini-games, which were always the generic Target Tests. Brawl also had a serious issue with how hard Trophies were to get compared to Stickers. Not returning Grab The Trophies was one of the worst decisions for that game. Ultimate doesn't suffer from this, at least, due to a better designed Classic Mode overall, and also has Spirits in general fairly easy to grind. Getting specific ones can sometimes be more difficult than it should be, but at least there's only one collectable, so while it's more of an illusion of being less annoying, I'll take it over... nothing.
