I rarely see Adyen mentioned in those HN threads. They might not be as big as PayPal or Stripe but in my experience they are really good.
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At first glance some docs look good but when you go to use it, it's confusing/incomplete/outdated