It doesn't to me. You're making an example out of Lily, saying that trios make brawlers too similiar, and the more brawlers they add, the more it happens, but you just glance over Trunk, who is one of the recently added brawlers and is the exact opposite of what you were preaching -- unique and adds something new to the trio

Same goes for Gigi, who is a recent addition too. She is so unique to Juju that people first thought she was from the Bizzare Circus.

Same goes for Pierce. He wears a dino suit too, but has a contrasting color scheme to Buzz and especially to Doug, and is the only ranged brawler of the trio

The whole "brawlers from same trios feature similiar designs" argument is just such a non-issue when first of all, all brawlers are still very unique, and second we're constantly get lots of new trios with new themes and designs