Some thoughts on various claims:
Incineroar was a bad choice.
I don't think it would have resonated with players if that were wholly the case, though there are better choices, and I would agree with the sentiment that nobody would want it if it never came.
Incineroar doesn't really have anything going for it.
This is just straight up not true. I could agree that it's the third weakest link in the Pokémon roster, but it's current relevance isn't nothing. In fact, I'd say it'd be practically everything if it belonged to a different franchise. lol. As far as its chances of returning goes, I think that Incineroar will do so intermittently, skipping a game or two between appearances, but appearing often enough to never truly become ridiculously surprising. Honestly, that probably applies to most of the oddball/underdog characters on Ultimate's roster, but that's an entirely different conversation.
Incineroar doesn't do anything that another wrestler wouldn't.
He kinda does though? His exact kit with Alolan Whip, Revenge, and a ton of really good normals gives him a dynamic that other characters wouldn't replicate due to it either not making sense on them, or the characters in question having gimmicks of their own that would end up happening. For example, Zangief would be playing Street Fighter, making his movement a lot less fluit, and would lack Incineroar's burst movement and probably also his good frame data. Haggar would likely have a focus on items due to his beat 'em up inpiration, ending up as a heavy that acts a bit more like if Bowser was an item character than Incineroar. King would have Tekken mechanics, making him kinda complicated to play, and very much ground based.
These characters are also just not very likely to be added any time soon, so IMO I'm glad we got something like this now.