The owner of Gumroad is a millionaire, but for some reason decided to crank up the cost of charges from 2.9% to 12.9% a few years ago. Needless to say, most people who don’t like being screwed switched to Stripe or another provider. That’s all you need to know about Gumroad.
Given they're a merchant of records, cost of compliance increased, mainly thanks to europe (that seems to have as a mission to ruin working people' lives as much as possible).
Stripe + Lemon Squeezy was a competitor.
Paddle is a competitor (which I use precisely to avoid having to deal with worldwide regulations) and they charge around 5%.
Gumroad also gives you a marketplace so there's some extra value.
I pay 25% for another marketplace, so 13% is not that crazy if they can bring you traffic.