At least the Omnipay drivers supported by the ai-payments extension are working because somebody has tested them and fixed issues if there have been any:https://aimeos.org/docs/User_Manual/Administration_Interface/Service_list
Many Omnipay drivers have been made for a project, work well there and fulfill the Omnipay interface. But this doesn't mean that they are fully compliant. The problem is that each driver requires individual settings and in combination with the payment gateway in between, this makes it difficult to test compliance automatically. Thus, it's most of the time a hands on job to fix issues and get them working.
On the other side, Omnipay and the drivers are Open Source which means you have at least the chance to fix it. I know the situation in the Magento ecosystem where many payment extensions are complete crap or you have to pay for them.
It doesn't make sense to complain about that something isn't working. Fix it and open a PR in the repository so everybody can participate from the improvement. If you can't, pay someone else who will do it for you. You are building an online shop for someone who wants to make money from it, so they should be able to invest a few bugs - especially as Aimeos is free of charge