A couple of days ago, Showdown made the teambuilder use the models from Pokemon HOME if 3D models are used in-battle. Many people (myself included) dislike how the HOME models look, but also like how the 3D models look in-battle. I understand that the team is currently working on making the HOME models look a bit better in the builder, but I think a good solution in the meantime would be to let players change the type of models/sprites they see in the builder independently of the models/sprites they see in-battle.
Mockup created using Inspect Element; could probably add an option to make it so that the sprites automatically change depending on the generation selected
Mockup created using Inspect Element; could probably add an option to make it so that the sprites automatically change depending on the generation selected