The respawn rules need work too (What's the point of killing a red monster if it's going to come back anyway?) and like others, I'm far from convinced that the conversion kit has balanced the monsters at all well.
The thing about the CK is that it was mainly a gimmick to attract players of first edition to start buying second edition. Awesome sauce in abilities makes it more tempting. Balance was not the primary focus during design. In that regard, the CK was really more like a promo than a true expansion.
The fans (even those who didn't own 1E) loved it for the added variety of monsters. They wanted choices, not balance. (Maybe they wanted choices AND balance, but beggars can't be choosers, right?)
I said back when 2E first launched that the appeal of the CK for variety would die off as more 2E expansions came out. There was no doubt in my mind that such expansions would come out, although I admit they've been coming a little faster than I expected. And now that more proper 2E variety has been added, people are starting to look at the CK monsters (and heroes) with a bit more critical eye, and realize what's happening.
Mind you, expansions will begin to show similar power creep in time. Some might argue that they already have in a few cases. That's what continuously expanding products do, they get more and more powerful over time in order to keep consumer interest. The CK just kicked things off with a bang for D2E.