Airbnb offered an unfair advantage (venture capital and centralized) in cornering the market on a streamlined platform, vs decentralized bnbs. Then when covid came, the individual bnbs operating on a tight margin shuttered, while airbnb prevailed (with massive layoffs). Both the hotel industry and airbnb were able to jack up prices due to loss of competition from mom&pops.
I can’t answer your second question.
Going from WhatsApp to Signal there’s literally no problem with Signal UI.