Exactly, I don't think you could have explained this any better.Think about it this way , instead of having one drive for the OS ( internal memory ) and one drive ( SD Card ) for media , it's going to have only one drive with the OS and a media folder on the same drive and partition instead of the SD Card , you will be able to access this via MTP .
This is not a bad thing at all , before if the device was mounted on a PC you weren't able to access the SD Card , apps installed on the SD Card , music , pics etc. , now you are able to access those files simultaneously with the PC and phone while copying data to the SD card . No need to mount the drive from the drop down menu , just connect and voila . No need to safe unmount .
And if you think it's a downgrade from the previous phones cause you won't be able to see the whole partition , thus the OS folders it's not at all . You weren't able to see the OS folders with the previous phones either cause they were on a different drive that was not mounting to the PC using UMS . All you could see was the SD card which was a media drive now replaced by a media folder .
You are still able to use Root Explorer to see the system folders from your phone if you need to . You can still use ABD to change system files on your phone from Windows .