Rey is not OP.
(And she's not that tough to farm, either—not like a FOTP. As soon as I could, I started working her hard nodes everyday and putting every guild currency I had toward her. I had her seven-starred in not very long.)
Rey is a simply straight-up damage dealer that can't survive long if she's focused on. She has no synergies to offer anyone. (Most other glass cannons give you nice synergies.)
Even with a fairly decent old meta team (Phasma, GS, QGJ, Rey, RG), I don't really have much success against new meta/wiggs. I'm not seeing her as frequently on my shard, even at 150–200 ranks where I usually hang at. That doesn't sound OP to me.
In fact, I think Rey has arguably kept the game balanced.
I'm 100% FTP, and paying players get a lot of advantages (as they rightly should, or else no one would pay): more refreshes for quicker farming, crystals to pick up raid gear quicker, access to Sun Fac and B2 back in the day, etc. Rey gives the FTP player a decent chance to keep in the same league with PTW.