You should check Opensea, where most popular NFTs including Runis have a 5% fee which is charged on top of the 2.5% platform fee. Most people are paying 7.5% plus gas fees which is often a flat $10-12, which sometimes go to over $50 during periods of higher network activity. Despite these fees, Opensea has pulled billions in volume over its lifetime.

In terms of simply staying at 5% fee and giving 2% to burn, marketplaces will lose 40% of revenue which I don't believe is fair. With a 4/2 approach, everyone loses a little bit for the greater good of the ecosystem. This is all detailed in the proposal.