Earlier quoted context omitted.
There aren't that many hurdles. 1. You download the apk 2. When you try to install it, it tells you it's from an unknown source and the installation was blocked to protect you 3. You tap "settings" and flip a switch to allow installing apps from your browser 4. You go back and tap "install". That's it. It's done. And you won't need to go to the settings the next time, it'll just work.
The main hurdle is that (without rooting) there doesn't seem to be a way for alternative app stores to silently update software. That's bearable though unpleasant when you have one or two pieces of software that rarely get updated, that's absolutely impossible when you have 10+ pieces of software - you'll sit there for 5 minutes just approving install prompts every week, which isn't something a normal human is going…
Does this actually matter? On the desktop it's normal for apps to update themselves. Is there some fundamental reason an Android app cannot do this too?