Thomas,
My agency just switched to the 9m.m. and I am fine with it. I think the main reason for switching was getting people to qualify, especially on the first try (the ammo shortage effects everyone).
Also, when we first went to the .40 S&W, we used a really hot load and had to replace all our BERETTA 96's after about 10 years. The new guns, H&K P-2000's were much smaller, about GLOCK 19 and 26 size, so the complaints about the BERETTA being too big went away, but qualifying was not easy. We down-stepped twice, going to a lighter bullet at the same velocity and then the 180 grain FEDERAL HST, which gives very good performance without all the noise, flash and recoil. However, high performance ammo, like HST was not available when we went to the .40 S&W, so we did it the old fashion way. We lightened the bullet and kicked up the velocity.
Still, a 9m.m. has less kick and recoil effects how easy a gun is too shoot.
Off duty, I shoot both 9 and 40 and have guns in both calibers. Every once in a while, I will go out and shoot our original hot load, a 155 grain bullet at 1200 fps and be reminded of how much easier it is too get a smaller, tighter group with a 9m.m., even though the 9 is a smaller gun.
On another post, I stated my opinion that agencies care more about getting EXPENSIVELY TRAINED PERSONAL to pass a qualification, than stopping power. It is easy to understand from that perspective. The .40 S&W, like any other caliber with more recoil than a 9m.m. will have the same qualifying problem as any more powerful round than the .38 Special, like the .357 magnum.
I think the 9m.m., like the .38 Special, strike a balance of recoil, gun weight and size that appeals to a very broad group of shooters and even non shooters who have decided to own a gun for self defense.
Jim