GK is one of the hardest toons in the game to get. All of the other toons you can buy or farm. Yes, arguably expensive, if you have to buy the 1299 pack, or even with Chromiums or at 80 crystals a shard, but you can buy them, unlock, and 7* them fairly quickly.
You can't do that with GK. You have to not only get a guild that can farm heroic tank raid, but also wait around, collecting 12 shards a week for two and a half months just to unlock him, and then again to 7* him.
As a single character that you are forced to wait about 5 months to 7*, I certainly hope he's a bit OP. Raid Han was also a bit OP for his time. Before auto taunts, if you had Raid Han you could basically choose who to shut down (Biggs most likely, or STH) and then your Biggs could go first and take out the first toon. That was OP, too. As well it should be. It's a little unfortunate that auto-taunt came removing his effectiveness.