I don't think it's the vast majority. Stripe charges ~2.9% + $0.30, and seems like Mastercard / Visa are probably taking around 1.15% + $0.05. So the vast major

I don't think it's the vast majority. Stripe charges ~2.9% + $0.30, and seems like Mastercard / Visa are probably taking around 1.15% + $0.05. So the vast majority should still be going to Stripe.