Well, the double thick handmade belt over powering a store bought holster isn't all that surprising.
I have the same DeSantis holster and it's not bad for a standard, off-the shelf commercial offering, but I prefer the Kydex paddle I ordered from Comp-Tac for the gun.
My DeSantis has the thumb strap, though, since I didn't get the M&P compact with thumb safeties. Is yours open top of with a thumb snap. Just curious.
If I were going to carry the M&P compact all the time I'd probably order the same Done Hume holster I've used for plainclothes and off-duty for many years, their H726, what they used to call a semi-open breakfront. The gun is held pretty securely (thumb snap), the leather is thicker and the DeSantis holsters I have, and the metal wire spring reinforcement and the low-cut front opening seem to aid in both easy presentation and reholstering.
A word of warning on reholstering ANY pistol made with a light trigger pull weight (and especially one where the mechanical safety is incorporated as part of the trigger itself), though. Paying attention to preventing the thumb snap retention strap from becoming caught in the trigger guard (or a jacket/coat cord, drawstring, tie, etc, for that matter) bears some consideration.
http://www.donhume.com/index.php?main_page=product_info&cPath=67_357_400&products_id=49
I have a bunch of this model holster for several pistols (they stopped making it for revolvers many years ago when I first discovered it, unfortunately).
The older versions had tunnel loops for the belt, while the new ones have plain open slots.
The newer ones also use a plastic cap to cover the inside of the retention strap's snap, but I found this to sometimes catch and hang up on the trigger guard. When it got pulled off one day I got out some of the cloth adhesive 'dots' the used to used to cover the back of the snap and used that, instead. (I asked for some many years ago and they sent me a few pages of them. They're apparently produced for some other purpose and are bought from a vendor.)
Here's an older H726 with my CS45. This one still looks good after several years, but it has only seen occasional use. I just don't carry the little .45 as much as I used to carry it (and I have a neat little special ordered Blade-Tech belt holster for it, too). I have an older brown one that's about as well worn as a pair of good boots. I used it for work & off-duty for quite a number of years, and it still sees use when I carry one of the guns it was made to fit.
I was first interested in the H726 after a should injury. The low cut/spring reinforced front makes for a fast and easy presentation. The muzzle clears when it's still below the belt line. It doesn't provide the protection against dust & blown debris that the pocket holsters can, though.
They aren't as affordable as they used to be ... but what is anymore?
The Comp-Tac standard paddle is a stout piece of plastic and pretty comfortable in the shape and distribution of the paddle. Nice folks with whom to deal, too. Not bad for a general range & work holster for my needs. They make it in a belt holster, too.
http://www.comp-tac.com/product_info.php?products_id=53
http://www.comp-tac.com/product_info.php?products_id=66
I gave up on the IWB idea some years ago. It was long rides on my motorcycle which finally pushed me away from IWB. I have a bunch of them, leather and plastic, from over the years, though.
Luck to you.
Sounds like you need a suitably better made holster to match your better belt, I'd think.
