Earlier quoted context omitted.
It basically is always cheaper for almost everything than Stripe (except AMEX). Interchange++ is always less than Stripe's equivalent charge (2.9% or lower for European cards) and 12¢ is less than 30¢. The page I agree is confusing.
Bear in mind, at any meaningful volume, Stripe does IC++ too and it isn't expensive edit: Looking at their (listed) acquiring and processing fees, Stripe appears to be cheaper That said, I don't know how Adyen's support is, but sadly Stripe's is honestly absolutely crap. Every single support interaction I've had with them has been incredibly slow and incredibly painful.
Adyen for example for Mastercard: €0,10 + Interchange++ (average total 0.90% - 1.10%)
Stripe advertised in Europe for Mastercard: €0,25 + 1.4% of transaction.