Although it does not mention any vegan variation, there is a wikipedia article about the "completos".
Mixing breadcrumbs into meatballs doesn't undo the texture of the meat itself, and different kinds of meats have different textures. Turkey, beef, and chicken meatballs all have different textures for example. The structures in the meat also change as they are cooked.
It is like how califlower rice isn't the same as regular rice, and there are a bunch of different types of rice. There is just a lot of complexity that means substitutes are always going to be a little off compared to their inspiration and to be honest that should be embraced and leaned into as an alternate instead of a replacement. Like a bean burrito compared to a beef or chicken burrito, they are all burritos but each one is their own thing.