FWIW, I have qualified on both 9 mm Glocks and M&P9's and have no issues using either type.
Facts matter...Feelings Can Lie
They weren't fixed in 2013. I had a 9mm CORE PRO that did 8-12 inches at 25 yards. Sold it to someone who only shoots at 7 yards and is happy with it. My old Smith revolvers do 4-6 inches at 50 yards.
I don't get the conventional wisdom about poor grouping only at longer range (25yds).
That hasn't been my experience. My 5-8" grouping guns still grouped poorly at 7 yds, it's just easier to discern the problem at 25 yds. Basically its easier to see and notice a grouping problem at 25, than to realize that a gun that barely does 2" at 7 yds is a problem. Math, angles, geometry and all that...
Example, I've been practicing the frank garcia dot drill...shooting 2" circles at speed. My M&Ps have a hard time keeping them in the 2" circle at 7 yds...at any speed (with still lots of vertical dispersion).
I have a much easier time at the dot drill with the P30. Despite the heavier trigger, snappier recoil, the gun doesn't produce fliers (only I can do that).
FWIW, most of my M&Ps group problems were with vertical dispersion...typical groups would be 2" wide by 5-8" tall at 25 yds (5 shots).
Its easier to see the issues at 25 out of a competent shooter. Most don't pay attention to accuracy problems (tiny bits of deviation) at 7 yards (unless they are expected shooter induced issues), so kudos to you for noticing it. Honestly we have kind of beaten this subject to death on this site and all I can say now is I hope you like them and they work for you.
Those people are clueful engineers, and they say there are machining issues in the slides.