Every input is delayed by your connection to the service. The signal going to the service and the signal in response from the service. That isn't even slightly comparable to buffering, which is just a momentary interruption. Because on PSnow you're getting that delay every single moment. The two issues aren't even comparable.
And I am not arguing that that lag makes the game unplayable. But I'll probably never want to experience an online FPS that way. So you hit forward and it tells the PSnow server that then signals the game server which then responds to the PSnow server which then signals your PC that you've moved forward. There is an extra several steps in games that are about timing... seems very very bad tbh. And as I said, if I do try the service, I'll have to see if this is how it turns out but I expect it will.
I've tried streaming games online before with an older service, that service doesn't exist any longer (AFAIK, I forget the exact one).