Bert,
It certainly seems that way especially seeing your impressive images with the 5DH. I think the Sigma is a nice lens but my expectations were very high in part due to some of the excellent reviews I've seen.
The fast (2.8) Canon non-IS lenses don't seem to perform well as seen by these results by Jerry Lodriguss:
http://www.astropix.com/HTML/M_DAP/M004/M004.HTM
There seems to be a few problems with centering of lens elements in the f2.8 IS designs.
Terry