Of course it's not a strategy for the WHOLE game
It just works really well up until about the time you set off for the south east.
And even after that, it's a pretty good way to weaken/finish a boss (as long as you can syphon MP/are stocked up on ethers/have MP regenerating equips/whatever ).
Plus he's going to be in for a hell of a rough time when he starts needing to buff his characters, considering his lack of reserve MP tanks.
And if he decides to get all of the summons, marks, and hidden bosses, well....
He's fucked, basically.