I'm not disagreeing with you by saying this, but I can imagine Apple sweetening the prospect by adding an AppleTV "Pro" to the ecosystem that will play intensive iPhone games like this with controller support. Tack-on MacOS playability as well and 1 purchase could mean you can play your save no matter where you are, across any platform within the ecosystem. Again, not saying this will happen. Just imagining how it could go.
I think that's definitely what's going to happen. The gaming market is going to see some huge disruption in the next few years as companies who didn't want to bother with the console market can start an ecosystem based around platform agnostic stores/ecosytems.