My experience with the G21.3 is the same. I consistently shoot better scores in GSSF matches with it and the gun feels like a brick to me. I wonder why this is? I hear it told that the Swiss Sig P210s had no issues with accuracy so I've not been inclined to think 9mm was all that different from .45ACP as to "inherent accuracy". But does the .45 actually have an edge?
ETA: I also have heard that the M&P 45 was originally designed to compete for the military's replacement of the 1911 and that they tightened up the tolerances to comply with the accuracy requirements. If this is true I could see S&W just running with it once in production. Can anyone confirm this?