The Stripe rate is a careful blend. There are many cards that are cheaper to process and there's probably a few that are more expensive to process at that rate, it works out in the wash in favor of Stripe. Also, that 30 cents is a large percentage if you're looking at a $5 transaction, for example (6%!)

See the "raw" rates here: https://www.mastercard.com/content/dam/mccom/us/business/doc...