If you do it with MB open, I think it actually does detect the folder changes. I remember seeing something about that.
If you don't have a lot of play history or haven't created a bunch of playlists that you'd worry about losing, yes, recreating the library from scratch is probably the way to go.
If you have data built up in the library that you don't want to lose, your options are to move the files back to where they started and move them the right way, to use the "Relink" utility to remap them in bulk (you can do this multiple times with multiple folders if there are just a handful) or to use the Tools->Locate Missing Files utility.
not maintain a library like Google music does
MusicBee is a library manager. It's going to maintain a library.