There is nothing "wrong" with graphite. Graphite just isn't quite as accurate as steel. I firmly believe in having your graphite shafts spine aligned - forget about how the graphics line up, I want consistency.
Graphite tends to hide slight mistakes, where steel won't. Every swing mistake is going to show up more with steel. That's been my experience, and it may be why you hit your irons straighter with the graphite than you were with steel.