I need to ask this why did they bother with MTP? I have had nothing but problems whenever that thing has been enabled.
What was wrong with usb mass storage?
**This is not all technically correct but is good enough to understand

It allows you to communicate with other objects (like tablets) in a way that USB Mass Storage cannot and it's fairly standardised. Hell, you can plug it into Emirates planes and it works which is kinda neat I guess. It also allows them to undo their HUGE bodge that they had to do.
Back when Android was concieved the memory card was the only user memory so just mounting /extSD over USB MS was easy but when internal storage came around they started having to rename /extSD as internal (as apps storage was pointed here) and extsd/external_sd as the SD card. This is a horrible, horrible bodge that can cause huge issues and long term this was a very bad thing (tm).
The fix was to mount the entire device storage through MTP and then put /extsd and /externalSD under the root of the MTP mount. The problem with MTP is it has things like folder locks etc... but technically it's better than USB MS as at least you don't have to completely unmount /extSD on the phone (which is what mass storage required*). it's better for users too long term. It works mostly like USB, works for more than just PCs which is how Android is truely visioned and while it can be annoying - a reboot fixes virtually anything.
*Technically it's possible to mount /extsd over USB and internally to the phone itself at the same time but it is possible to do some truely bad stuff doing this so it was usually a developer type feature used in some ROMs.