Considering Apple intentionally slows older phones with firmware updates post new phone release, I think your argument that they're trying to protect the experience doesn't hold much weight.
Please provide documentation for this. The only one I know if where they detected degrading batteries that would cause sudden shutdowns, and (without telling people) throttled the CPU to prevent the sudden spike of power draw that was causing the shutdowns. Certainly not a perfect reaction, but very far from your assertion.
I’m sure they do it all the time, but this one incident actually caused worldwide news-coverage, even in tabloids read by normal people (that is, not just techies).
That isn’t “intentionally slowing phones with new firmware releases”.
That’s the phone slowing the CPU when the battery gets old to prevent unexpected shutdowns. If you think this is “planned obselence” you misunderstand the issue.
iOS 11.3 now lets you disable this, so you can have full performance at the cost of unexpected shutdowns. Or you can just get an official battery replacement for $29 and your phone will be like new.