Part of the problem is that so much of our “software” is now just weaponized webpages.

And so there is no “staying on windows 7” for SaaS.

It's better than nothing, but it isn't really sufficient. Typically, the "stable" channel still releases too frequently.

What would address my concern is if it were possible to skip releases, however rare or common they are, as I wish. But that raises an entirely different Bad Thing in the modern software industry -- that security updates are increasingly inseparable from other updates.

It can in some contexts, but I've never seen a "release channels" approach for e.g. a configuration UI. I'm not sure if that's because it's fundamentally incompatible with business needs or it's just not something UX devs are aware of.

It adds a huge support burden to devs and UX, as they need to support an increasing number of different UX versions or basically never change anything (which is bad for their career).

Supporting multiple versions adds a huge burden, for sure, but I'm not sure it's bigger for a configuration UI or webpage than it is for any other application that has some kind of backend or data shared across the versions.