Input lag while streaming is not that bad on a good connection. It won’t work for online FPS games (at least not if you want to win), but for slower FPS, RPGs, etc, it’s ok. This is based on my experience with Geforce Now, I haven’t tried Stadia.

As for the business model though, you’re totally right. No way I’m going to buy a game and be locked into Stadia. Not only would I be prevented from playing locally, who knows how long Stadia will be around at this rate?