The amount is suspiciously close to the standard frontend fee, around 0.75%

Is Rainbow collecting roughly a 5-6 USD fee on a 750 USD swap? Is this standard behavior?

yep! 80bps is pretty standard across wallets

I work at the posts office

terminally.online

I get why wallets and centralized frontends monetize like this but it does force everyone who is fee sensitive to have to jump through hoops.

This is like Google finding out that showing low quality and irrelevant results makes users spend more time on the platform. It misaligns incentives.