I agree, this could be improved. Changing the order of the songs in playlists is time consuming.
I would also suggest that when tapping on the "+" button to add songs in the playlist, instead of just having to choose "new song" or "from library", it would very convenient to also have a "from playlists" option (then we can select from which playlist we wish to add songs). That would make things much faster to rearrange songs in playlists.