I've got a fairly early M&P9 full size with the smooth profile second generation barrel without dimple(s). I believe it's the slower 1:18.75" twist rate. Seems like it starts to unlock with any rearward movement of the slide too.
I've never bothered to bench rest it, but with the Apex FSS and trigger I've been pleased with how well it shoots with both 115 grain and 147 grain stuff. Shot side by side with a G19 and a VP9 it shoots essentially equivalent groups. The Glock and the VP9 might edge it out if I had more trigger time on them, but it's a toss up. I think my USP9 and CZ75 edge the M&P out slightly, but by no means would I call the M&P "inaccurate". I will say that it was difficult to get a clean break with the stock trigger on the M&P, resulting in poor apparent accuracy. The newer M&Ps supposedly have much-improved triggers so this may be less of a problem now. I will say that putting the latest trigger bar and slide stop in my M&P did markedly improve the reset.
Now, I'm not a great handgun shot, but after watching every other person on the range whose target set at 7 yards looks like it was shot with birdshot at 100 yards, I think your average shooter is not going to be able to notice any accuracy problems with the gun...