I know it's changed recently, but for quite awhile the answer to "what can I do on Android that Linux on mobile can't" was "make a phone call."
That class of product issue is why FOSS is different than the marketplace. It's often behind in creature comforts/UI/UX and lightyears beyond in technical capability. Because FOSS developers spend time on things they care about, not about what the market does.
I prefer when FOSS piggybacks onto larger projects. F-droid is amazing, I have all the comforts of real android and the nerdy stuff from FOSS and root addons. I get the best of both worlds, great hardware for the price, great support from a good UI, and great support from the ports of CLI and nerds who also like to have their android phones be real linux computers.
That class of product issue is why FOSS is different than the marketplace. It's often behind in creature comforts/UI/UX and lightyears beyond in technical capability. Because FOSS developers spend time on things they care about, not about what the market does.