she had the Phoenix then, in normal circumstances she wouldnt be able to kick thor's ass.
I have the theory that Morrison intended Emma's diamond form to be much stronger than what future writers made her to be. Jack o Diamonds, a telepath criminal with diamond skin who had Cyclops as his protegee for a while when Scott escaped from his orphanage (the 60s Stan lee run), could cut steel beams with his hand and beat She Hulk when he was resurrected as a zombie in the 80s. It seems to me Morrison was inspired a bit by that when he decided to give Emma the diamond form. And iirc, he did that (emma's diamond form) because he wanted to use Colossus but couldnt because he was dead (he died for the cure of the legacy virus, marvel didnt resurrect him until whedon), so he must have done it thinking it would make her Colossus tier.