Yeah. Hydreigon is. All the pswado (sorry if spelled wrong) legendaries are, a total of 600 is equal and sometimes higher than some legendary Pokemon's stats. An example for lower is Cresselia and an example for equal is Jirachi,Mew,or Celebi. It's lowest stat is 90 which is the highest for some Pokemon so I would definitly say yes.Plus it has a wide movepool. With a lot of strong moves to make it very powerful it dominates most non-legendary dragons all over Unova, and in other reigons.Plus he's not in Ubers (which he should be in)so he dominates. I'm actually suprised GameFreak didn't put the pswados(Still, sorry if spelled wrong)in the Uber tier,because darkrai,Deoxys-A,Deoxys-S,and normal Deoxys all have 600 total base stats. Which is exactly the same for all Pswados.There's a reason everyone wants a hydreigon,it's movepoool is sooo wide it can have HUGE type coverage with Earthquake,Ice Fang,Focus Blast,Dragon Pulse,Surf,Flash Cannon,Flamethrower, and a couple more.Out of the 93 generation 5 TMs, Hydreigon can be taught 41 of them. Mor than half!So due to hydreigon not being in the Uber tier,hydreigon is definitly OP, along with the other pswado(still sorry, I need to look that up)legendaries.