Relevance means nothing.
See also: Rool, King K. and Zazooie, Banjo and
This isn't about "relevance" , it's timing.
Furthermore, all of those characters you mentioned only further prove my point, because all of them were large requests from the Smash Ballot, which happened in '15 (the Ballot ended in October which was only 2 months before the Smash Ultimate Project Planning was completed) plus Phil Spencer's word about Banjo in Smash. Also we know that Steve's negotiations took almost 5 years according Daniel Kalpan (former MC production director). Smash games take a long time, and all of these events happened before Smash Ultimate started development, so they made these choices in advance. Im pretty sure all of these things happening years ago influenced Smash's roster, especially because they all basically happened during what was likely the roster being planned (Smash requests almost never influence the current games, they influence the FUTURE ones, which is why Smash Four's K.Rool support ended up helping for his inclusion in the next game)
Crash was still dead at the time, and Activision barely even flirted with the idea of bringing him back until at least a few months later, plus Activision never showd the same enthusiasm as Microsoft has when it comes to Smash (at least in public)
This is not so different from what happened to ARMS and Xenoblade in the base game, they may had stand a chance and not been for the fact that the game was well into development and it was simply too late for them in the base game. They managed to get a chance in DLC, but i don't think Crash will be as lucky.
It doesn't matter how "relevant" you are if you become relevant after Smash's roster plan has been finished, which is what im arguing about.
I'm assuming you mean Ridley, King K. Rool and Banjo & Kazooie, and I agree with you. I'd also put Simon alongside them since he was also highly-requested for a long time (though not to the same extent, I will admit), and Castlevania as a series hadn't been relavent for a long time before coming to Ultimate.
This is a common misconception, but it's completely false. Castlevania was still alive during the early plannings of Ultimate, just not in the way most fans want to remember.
After the low sales of the DS Games (Dawn of Sorrow, Portrait of Ruin and Order of Ecclesia) and the bloated confusing timeline that it had, the series was rebooted into Lords of Shadow, the most recent game was Lords of Shadow 2 in Twenty Fourth teen, the same year as Smash For Wii U/3DS, and a year before Smash Ultiamte started being planned out. and as for Simon, he was a main playable character in Mirror of Fate for the 3DS in Twenty Thirtheen, so if by Relevant you mean "Appearing in a prominent role in a recent game" you are pretty much wrong.
He was as relevant as you could imagine (and don't give me "BUT SIMON FROM MIRROR OF FATE WAS FROM A DIFFERENT CONTINUITY FROM THE ONE WE HAVE IN SMASH", because relevance's usage in the Smash Community almost always means "has this character appeared in a recent game", and Simon fit that definition, regardless of incarnation) but back then almost nobody talked about Simon in Smash because "one character per company" was a popular fan-rule at time time: "We already have Snake, why would they add Simon" was pretty much the common response, plus people didn't saw Snake coming back which only made reasons to talk about Konami characters even less popular.
Simon did not come into Smash existence in August 8th of '18, he was part of Smash's roster as soon as the game started development, and during those days it didn't seem as if Castlevania was going into a hiatus (it only became an accepted fact after the whole Konami Kojima drama)
IF Crash is in Smash, he already is part of the roster and we just haven't seen him yet, meaning that time timing may have late for Base Game but not for DLC, which wouldn't be a first (i mean i just mentioned how Xeno 2 and ARMS basically got a second chance thanks to this Fighter Pass) so i do admit there's till a decent chance, im just not counting on it.
As for Crash's chances, I still think he's got a very good shot for the E3 reveal.
This is Crash's saving grace in my opinion. Crash is a character who is meant to be a big reveal, so maybe they are waiting for a reveal at E3, and i think if there's any moment to reveal him assuming he is even in the roster, it's there.
I have mentioned how things in Smash are planned well in advance, so the idea of Crash being an E3 reveal wouldn't surprise me too much, although i will assume that in said scenario he is the penultimate reveal, as the last character reveals in Smash ALWYAS end not with a bang, but a whimper.