Is 16.17 really as bad as it seems? And how to downgrade to 15.19

There is likelihood this is a software problem as the "always wants to update" thing is a big red flag.

The other symptoms are indicative of a processor which is not running its internal task list correctly, getting stuck doing one thing.

But my point is that not everyone is seeing the always wanting to update but not able to connect issue, so that spends like a hardware issue and a processor issue as you indicated.

If you have a look around the forums, you'll find many people with the same problems, all appearing after updating to 16.17.

The heart rate issues people are experiencing don't have to do with using the tri-HRM.  Mine works fine as well.  It's the wrist heart rate that people are having issues with.  My swims stopped recording distance the next day after this update.

No issues for me. Mostly used for running with Garmin Coach, while using HR belt or Wrist HR. Making and following courses are good too. Other sports I do not know.

None for me either. However I've had the watch since the week it launched and progressed incrementally through all the betas and releases.

My guess is that the watches affected might be ones which have skipped many intermediate releases, eg. new watches which were part of the first batch manufactured in early 2022 but which only got sold recently.

Could be true. I have mine from nearly the launch, so yes, I had my updates one after the other and experience no problems.