Android was already a platform on life support. Google has wielded its authority to dictate how apps should behave such that even 3rd party stores do not stray far from Google's rules. Users of android phones have little hope to run a program from 5 years ago, or to roll back a bad update in an era full of bad updates.
Android used to split storage into various partitions, which is why this used to work - It was able to unmount the partition and let your PC manage it. This meant any apps using that partition needed to be stopped, etc etc. It was a pain, and I can totally understand why they moved away from this approach.
Personally I prefer the new way, yes using MTP has some limitations as you've noticed but it does mean the storage can remain mounted on android while your PC accesses it.