Alright, I love Decidueye. He's my Alolan starter of choice and I think he'd make a great fighter. But let's be real here, being an archer isn't as huge of a selling point as we think it is. Just look at this guy.
Yeah, archery is barely implemented into his moveset at all. They gave him a pair of blades to fight with so he rarely uses his arrows. But riddle me this; why do you think they chose to design him that way? He fought almost exclusively with arrows in his base game, so why did they feel the need to change that? It's because archer-based movesets aren't as amazing of a fit as we sometimes make them out to be in Smash Bros.
Projectile balance in this game is difficult, especially when you consider how powerful projectile camping can be in free-for-alls. Decidueye is able to focus on a long-range projectile heavy moveset in Pokken because that's a game balanced around projectile zoning - most characters have decent enough ranged options and even if they don't canceling counters into dashes is far easier to pull off then consistently perfect shielding everything. Smash Brothers tends to go far lighter on that however. It's why Samus likes to smack people with her arm canon and why Fox prefers to kick his enemies over firing his laser at them. Even with the recent Mega Man and Villager breaking those trends somewhat, a lot of their projectiles are still fairly short-ranged or weak. It'd probably be the same with Decidueye. His long range options would likely be fairly weak, slow or otherwise limited, and his moveset would focus far more heavily on mid-range to close-range combat, as is the case with most characters.
Don't get me wrong, I still think Decidueye could be a fun and interesting fighter, but I don't think the difference between him and Incineroar is quite as night and day as people make it out to be. At the end of the day, Smash Brothers is primarily focused on close range combat. It makes sense to me why the creator would pick a character who specializes in close range grappling.