The .40 S&W was introduced into LE use in 1990. In the 20 years since it's introduction it has acquitted itself increasingly well and has become a respected round in LE/Gov (non-military) service.
The sort of info which might be considered related to "hard data & research" accumulated and reviewed by LE isn't really something commonly or easily obtained by the general public.
Even some of the gel testing conducted by larger agencies isn't something commonly released to the public. I know of one large fed agency that will only release their testing to local LE agencies upon official written request of someone of at least supervisor's rank, and the last time I looked at the requirements it stated that it's not for release outside the requesting agency.
If the .40 S&W hasn't yet eclipsed the 9mm when it comes to general service usage, overall, and LE sales, it's getting very close.
Personally, I waited 10 years after it was introduced before I decided to buy my first pistol chambered in .40 S&W. By that time I'd had the opportunity to learn how well it had been serving the CHP here in CA and how well it was regarded by some agencies which had been using it.
I still like my 9mm and .45's, but I also now own 5 pistols chambered in .40 S&W and consider it an established, effective defensive caliber. It's seemed to increasingly be the most requested and tested caliber in the mobile manufacturer gel events which I've attended or for which I've received info afterward. It's arguably popular among a growing number of LE users for a reason.
Besides, you're always going to encounter local experiences and decisions regarding ammunition among LE agencies. I remember when I was discussing duty ammunition with an armorer instructor who was a long time working cop. He worked for a large agency back East where the weather was often cold and folks wore layered clothing a lot of the time. He said that they had switched from .45 JHP duty ammunition to .40 S&W ammunition because of how much better the .40 loads resisted plugging in some shootings than the .45 loads they'd used.
What does that mean? It means a specific agency decided to choose a specific caliber based upon their own unique experiences with a couple of calibers and how well one of them seemed to better meet their perceived needs. No doubt someone could find another agency who had acquired a different set of experiences and/or who made had a different choice in caliber/ammunition.
The .40 S&W has become one of the major LE choices in the years since its introduction .. if not the major choice by now.
Suit yourself. Everyone else does.
I'll keep my .40's, but I'll also still keep my 9's, .45's, .38's & .357 Magnum's.