It will be useless if they pay with USDT because basically USTD is using ETH network. You can see how fee that will be chargered if you send USDT in one wallet to USDT in another wallet.

This is the problem that we head, everytime a coin is increasing then the gas fee will increase as well. ETH will launch new system ETH 2.0 that can reduce its gas fee per one transaction, I think it will resolve for those who complain against gas fee.