He plays like Sonic in some games, but in lore he has tons of abilities that would make him unique.
As I said, his most iconic move is a time stop ability (which surprise! His AT uses it). Do you think making him a worthless clone of one of the most badly received movesets in Smash's history would make him justice purely because of gameplay reasons? (and again, he's not the only one to have ever shared similarities with Sonic in this regard and by that logic everyone else should be an echo too).
It's a mistake to think it would be for the "sake" of it when that's how he has been portrayed in cutscenes and some games as well.
Since you're asking me questions, I will reply to this once more... (but as the creator of this thread, I really don't want it to get so far off topic).
Yes, I 100% think characters should reflect gameplay, especially over lore and stories that do not affect character gameplay in home series. I have no idea why a characters moveset would be based on cutscenes in Smash, if they don't affect the gameplay of the character in their own series.
I don't know all of Sonic's games, but I know in Adventure Battle, Heroes, Rivals, he plays identically to Sonic. I know in games like Sonic 06, he specifically has the same abilities of Sonic (and otherwise DOES use attacks, such as the Chaos energy), but is primarily differentiated by the ability to use machines. In Sonic Colors, I don't recall him being at all different than Sonic (not that I have much experience here). In Sonic Generations, the only difference from Sonic's usual abilities is the Chaos Spear.
I do know Sonic is poorly received for his moveset, and I think the fact that Sonic was boiled down to his main features is another point in the face of why Shadow would be boiled down to the same mechanics. And again, if Shadow
couldnt do the things Sonic does, it would seem like they aren't even from the same franchise, nor would it reflect the core of playing Shadow in other games.