I really don't like arguing about the whole echo thing but I actually want a reason to play as Dixie and an echo wouldn't do that for me personally since I already love using Diddy who actually represents the move set to his character meanwhile Dixie who isn't the type who uses cartwheels or breakdancing style fighting, she's has always been reliant on her ponytail which is what made her popular to begin with and allow her to do many things that Diddy could never emulate.Why did they make retro Mario's hat and overalls orange instead of red?! I'd rock that outfit all the time in Mario Odyssey if it weren't for that!
I'd rather have Dixie than not have Dixie, personally. If Chrom and Ken can be echoes, I've no doubt Dixie could be an echo and still retain her classic moves and personality.
Plus I still believe if she's was available as one she would have made it in, also Diddy still has a tail ledge attack and Dk's up b would have to be heavily altered considering the different character structures, if Isabelle couldn't be an echo because her body design is different from Villager than the Dk's up b wouldn't work that easily.