I am not worried in the least bit. As other people have said, this is what Harden does. He is pretty much a fastball changeup pitcher at this point. He does throw breaking stuff occasionally but he pretty much throws those two pitches. Harden looks like a really smart pitcher and knows you aren't going to get by as a starter by throwing two pitches, so he throws fastballs with different velocities and it is clearly really effective as he has only had one bad outing since joining the Cubs.