The $7 amount is a 1% commission that we add for facilitating the on-ramp through Brave Wallet, and more importantly help support Brave and its free and open-source products.
As you pointed out, you can buy crypto directly from Ramp website without the affiliate fee included. Note that a lot of our on-ramp users are first-time crypto buyers and therefore prone to fat-finger errors. Using Ramp through Brave Wallet certainly reduces this risk.
I will follow-up with the team to make things more transparent in future.
Cheers!