Visa and MC could be L5 networks for Bitcoin, why not? Lightning is lower level and more decentralized, but it doesn't solve issues like dispute arbitration which credit cards do.
Settlement is among the least interesting problems that Visa and Mastercard solve for merchants and customers.
Yes, being able to settle across currencies pretty efficiently is nice, but the real value is just what you mention: Dispute arbitration and managing liability in case of fraud.
