The feedback form basically get 20% of total feedbacks about how do they don't like the new tab bar (see their github issue list generated from the proton feedback form). Consider how people are lazy about fill a proper form for just complain something. That is a lot.

Has something which made it into Beta ever been reverted prior to release due to negative feedback from users testing it? From the outside that just doesn't appear to be a thing they use the beta channel for.