The whole UI thing is confusing. While I agree that UI itself is a technique, what Goku has is MORE than just that. He shouldnt be getting a power-up from mastering self movement. Imo Goku is beginning to learn how to use a form that can make use of UI. Think about it, Whis can use ultra instinct, iirc we have seen him use it already when sparring with Goku and Vegeta back in RoF, and nothing changed in his looks.
For example, no one knows what the HEAT is that keeps emanating from Goku when in this new form, therefore its different to just UI is what im trying to say.
Vegetas is also a strange one. He looks just different enough and gets such a massive power boost that it cant just be full powered ssjb. His hair is darker and he has two tone pupils instead of just the normal blue.