>The only solution is you download stuff and it remains runnable and usable without any connection or authorisation to any service.

I agree, but that could still be done even when using a centralized distribution platform. I would say those are two separate issues. I think (not positive) that's the whole premise of GOG, isn't it?

>If the payment processor shuts your revenue down you can move elsewhere.

Not really, though. If the payment processor stops doing business with your company, your shit out of luck. Instead of pressuring steam or whoever, they just pressure you directly. The single (well, double) point of failure always chains up to the payment processors.