Debit cards are definitely better than credit cards in several situations, but most of them outside of various national schemes are still using the networks run by VISA, MC, etc.

The thing that bugs me is that we're perfectly capable of doing quick, reliable transactions without any need for cards at all today, particularly in Europe with the SEPA infrastructure, or in other areas that have national debit schemes. We just haven't got around to making this easy for both online and in-person payments yet, though things like the payment methods using smartphones and the consolidation of debit schemes that fintech firms like GoCardless are working on seem like obvious steps in the right direction to me.