Visa and MC are four party payment systems. In short, the fees paid on a transaction are split between the merchant acquirer cut (merchant service charge), the card network (scheme fees) and the card issuer's bank (interchange).

Stripe is a merchant acquirer and Visa/MC a card network.

The 2%-3% are the total fees imposed by a stripe, a merchant acquirer. The 0.3% is Visa's cut. After subtracting the card issuer's cut, what remains goes to Stripe.