Adyen is an "interchange-plus" payment processor, which means they pass on the interchange fee charged to them by the payment processing networks, plus a fixed markup.

Stripe is a flat-rate payment processor: 2.9% + $0.30 on everything.

Interchange fees range from 0.05% to 3.2%, more or less. Most consumer cards are going to be significantly cheaper than 2.9% to process. Many people use "check cards" from their bank which are in that 0.05% category, for example. American Express and the top tier Visa and MasterCard rewards/business cards are the ones where interchange can exceed 2.9%.

There are many "interchange-plus" merchant account providers now. I get better rates than Adyen is advertising on their website right now.