If i recall right, they are going to be redoing SP rewards from enemies. Getting rid of Phys Level means that we won't have the tons of extra HP/MP/etc we get from being 50 phys, so enemies will pose some challenge at lower ranks. They were also supposed to be balancing the game so that you are meant to solo xp off of same-level enemies and increase the xp they give, so I'm guessing that boost would trickle up to the higher level enemies too, who will be much more difficult.

Just remember that even if you beat a high level enemy, if you have to rest for a while after every single fight it slows down the pace considerably. Striking a balance between fighting and downtime is a challenge too =P