I believe it. Sig really has kicked Glocks ass on the 9mm "slim" guns, both in form/capacity, and marketing them. It doesn't hurt that they seem to work pretty dang well, and are shootable for lots of folks.
The M&P, and the Sig 320, both would be top competitors to knock the Glock 19 off its pillar. If the M&P 1.0 9mm's hadn't had the accuracy issues, and the Sig 320's hadn't had the drop safety issue, I think either one could have really taken the spotlight.