I hope their API and SDK got better. It was a pain to implement and use some years ago. Stripe was light years ahead and we ended up switching. Also the capital demands from Adyen were much higher than Stripe.
I think you vastly underestimate the importance of ease of use.
Management might also have a problem later in case of non-payment/chargebacks etc
But, in general, people need to look past the first impression
I really don't see how it's a hard problem either? How often does a payment gateway API really need to change? Just spend the resources necessary to get it right. If you really need to, hire (another) FTE on docs.
At first glance some docs look good but when you go to use it, it's confusing/incomplete/outdated