anythingbutgrass, I'll explain the best I can.
In all truthfullness, there's no card that really "destroys" consistency. There's always a chance you'll still draw well throughout the game no matter how few consistency cards you have. However, that's not going to be the case most of the time, meaning the more consistency cards you have, the higher your chances are of drawing well.
And this brings me to cards like Hammers. While they might seem good (and really, they aren't a bad card), they are outclassed by more consistency. Darkrai/Hydreigon almost doesn't have enough room to fit the normal deck stuff in, much less extras like Hammers. You can say it's part of the main strategy of the deck, but Hydreigon functions plenty fine on its own without having separate strategies like hammers. 99% of the time you draw a hammer when using that deck, you're going to have wished it was a Juniper, N, or Random Reciever (or some other supporter). I know this from extensive testing (I was playing it before DRX was released).
Your argument that stuff like a Mewtwo and DCE are very common is well taken, but keep in mind you can often beat that without the use of something like Enhanced Hammer. Even if Enhanced Hammer happens to be your one ticket out of that situation, your just going to be a a deeper hole if you don't have the supporters you need. As an example, I run 15-16 supporters in pretty much every deck I play and I STILL don't draw the cards I want when I want them.
Overall, what I'm trying to say is that Enhanced Hammer and other cards like it are not necessarily bad, but are outclassed by other cards you could put into the deck to help it carry out it's primary function.