I help maintain the phones/computers for several non-technical and/or elderly family members.
Their computers are a mess. No matter what pro-active measures I take, every time I get involved, they have a bunch of nonsense installed doing who-knows-what. Random apps, most of which are running all the time, slogging down the system. The younger folks have different game-stores, or other similar things, all running in the background. The computers are slower than mud.
Their phones are all fine. They may download crap, but I know it is almost impossible for it to mess things up outside of that individual app.
I'm not saying this to completely defend Apple - I honestly don't know which side of the App Store/sideloading debate I fall on. I'm just pointing out that there are huge benefits, particularly for the general population of non-techincal users, to Apple remaining as a gatekeeper (albeit obviously a quite imperfect one).