The more the ecosystem opens up, the easier it is for them to accomplish their goals, regardless of how smart you think you are.
40% of the market has a completely open ecosystem with no restrictions on side loading what so ever, and they are doing just fine.
Just this week news dropped of big tech actively exploiting an Android issue to track you 'smart users' outside the 'safe sandbox' it provides.
Hint: A poor argument is built around whataboutism. But a really shitty argument is off topic. Tracking pixels and breaking out of sandboxes has nothing to do with sideloading, and in fact the effort that people go hacking around restrictions in the OS despite sideloading existing not only makes your off topic argument shitty, but it actually works against you since you're postulating that sideloading is somehow some easy vector into people's devices.
In the future try to argue for your case, not against it.
I really do wish Apple would fork their OS and segregate the hardware for people who do opt in to the walled garden.
Blink twice if someone is holding a gun to your head forcing you to sideload an app, we'll send help.