I do agree with your point, in particular with the last part about the grifters. But I think this was bound to happen, just as it happens in pretty much any domain that is no longer a niche. Companies see a way to make a quick buck and move in.
However, I see this as something of a new development that didn't actually remove what was before. You can still run Linux if you like, just as you could 10-20 years ago. You don't have access to UHD Netflix, but... you never had. They didn't take this away, it was never given in the first place.
Granted, the fact that Apple goes downhill is, I think, a net negative for the computing world. Ditto for the tracking embedded in windows 10.
Regarding Linux, there's the UEFI / SecureBoot situation, but even on "enterprise" HP hardware this can not only be disabled but I can actually load my own keys, so I don't perceive this as a threat for the moment.
The deeper problem, to me, is that all this works because there are enough people who, for some reason, don't care. Maybe they're not educated enough / don't know better, maybe they actually want it, maybe they're not aware. But the fact remains that there are many, many people who buy the iPhone, who use windows 10, who use facebook, who buy echos, etc. So, aside from "doing the right thing", what incentives do these companies have to stop doing what they do?
[] I actually do own an iPhone but I treat it like an appliance. I install next to no apps, so I really don't care about who can install what on it. I do care that my 4 yo phone got the latest major upgrade and it works as well as the day I brought it home.
However, I am pissed that LittleSnitch is unable to filter all traffic on my Big Sur Mac. But I basically no longer use the Mac, so I'm doing something about it.