I think you’re absolutely correct.

I suspect it is practical to do a small one-time run of maybe a 1000 copies of a purely hardware device and sell them. Of course, that is just kicking the can down the road a bit farther… At least dealing with obsolescence with purely analog parts is simpler…

As soon as software appears, things become less ideal. Now the HW and SW become highly specialized to a single vendor’s single family of devices. Plus, bugs and internet connectivity almost ensure a potentially unbounded number of updates or forever broken functionality. Even toolchains fade into obsolescence…

Sure, one can redesign for a new microcontroller from a new vendor. Maybe with new RTOS too. Of course, that is almost as much work as the initial design and probably done by someone else at a later date. Yuck!

(And I saw this as a software engineer!)

Definitely something to be said of the old habit of a simple analog design with schematics fully provided to the end user. This is something probably still needed today, but perhaps commercially challenging, especially with countries like China in play…