Is a browser on compromised hardware supposed to be more secure than an app? Amazon, steam etc still risk exposing accounts authorized to make payments using your money. It's easy to think "I just won't use banks" and underestimate the risks of doing anything on compromised hardware, and the answer isn't to play the "what could possibly go wrong" game, it's to not use compromised hardware.
I’m not really worried about mainstream Chinese manufacturers stealing my bank credentials. Fly-by-night budget phones full of crapware, yeah sure.
Also when I use my phone to watch something in a focused way, that's a high quality HD screen filling my field of view even better than a theater. The audio isn't quite as good, but the overall experience beats most TV setups. So unless you dismiss Netflix as a whole, I think your notion of the phone experience is overly narrow.