I mean there is more to the Pokemon than their typing. Inceniroar has tons of personality while Decidueye is a stoic archer when we already have a stoic ninja and a stoic monk/fighter thing. Inceniroar has the pro-wrestler moves and flair while Decidueye would be the 6th person using a bow. I still don't understand how anyone can be upset we got a fighter who taunts after every move and does a rope a dope.
Firstly, the Smash team has proven they can put personality into nearly anything. Second, Deciduey has just as much personality, just in another direction. Decidueye are typically proud, cocky and even prissy. Yes, Incineroar has his crowd rousing, but Deciduey could have just as many interesting reactions, like tugging his hood closed when he loses, or freaking out when hit by messier moves like an Inkling attack or a Wario Waft.
As for you comment on Decidueye being the 6 bow fighter... Firstly, three of those fighters use a bow for exactly one move in their toolkit, and of the 5 bow users, there are only two completely unique move sets among them. Decidueye would need a completely unique moveset and would utilize it's arrows much more than the Links and is ways much different than the pits.
And even if you still think that's too many bows, I put it to you that the over abundance of fire based fighters in the game is far more problematic. After looking over the entire roster, there were 26 characters who ad at least one fire based move (and this was actually being generous as I choose to leave out moves that cause fire due to explosion Letting the likes of Toon Link and Diddy Kong escape this list as well as others) I also left Ganondorph of the list by considering his attacks darkness based even tho they behave like fire does.
And again, you might say there is more to pokemon than types (which would be completely true) but it is the foundation they are built on and when there are 18 different types and over 800 monsters, it becomes clear that you will never be able to represent all in a game like Smash, Which makes all the move reason to pick the most divers one you could for the roster when you are only going to feature a handful.
It's the same reason why Fire Emblem fans are frustrated that every fighter they get is a sword fighter when swords are only part of what the games offer.
I'm not angry Incineroar is in, just disappointed as there could have been better picks that would have provided more variety.
Now in elemental representation, fire far outweighs all the others in this game. There are three water based fighters and two other fighters who have a single water based move (Mario and Isabelle) and there are three plant based fighters and one other fighter with a single plant based move (villager's tree) Even trying to give plants the best case scenario you could try and include Lucas' stick attack and if you really want to stretch it you could include Peach and Daisy's Toad counter (tho i don't count that as Mushrooms aren't plants)
So I would say having one more plant based move set (with the addition of Ghost based moves which aside from Shadow Ball and Shadow Sneak is untapped potential) would ad far more variety than the 26 fire based character did.