Brad, first & foremost - ggggGGGGO 'Cats! Now that the important stuff is out of the way, the belts you wore before getting a dedicated gun belt may have been better than terrible. So the differences may be more difficult to immediately recognize. IMHO, the reason for a good gun belt is more than just a snug, repeatable holster position. It's partially insurance AGAINST belt failure. A broken (cast) buckle or popped stitches isn't too big of a deal if my belt is just holding my jeans up. But if it's packing a couple of extra pounds of pistol and spare ammo to save my life and I've just been knocked onto my back on an asphalt parking lot, that's a VERY INCONVENIENT TIME to discover that my cheap Levi's belt wasn't up to the task. To me, my gun belt is a link in my self-defense chain. Making sure it's a STRONG link isn't expensive. But a failure at the perfectly wrong moment sure could be.
I'm going to toss my opinion out in favor of gun belts, I didn't believe in them for years but once I got my first good one that worked it made a heck of a difference for me. That's actually why I started building them, I actually don't particularly like making gun belts if I'm honest, but I think they are necessary for most any holster design.
The main purpose in my mind of the belt is spreading out the weight of the gun over a larger area, particularly helpful on heavier guns and guys who don't cinch their belts down. On the weight front your looking at two factors, vertical strength and horizontal, on most gun belts it's very strong vertically and fairly stiff horizontally. This allows the belt to carry the weight of the gun across a larger area compared to a more flexible belt. So rather than carrying the weight on that 4-6 inches around the gun/holster you spread it over at least double that area. It is true with an IWB rig you won't have nearly the issues with the grip of the gun tipping out like you will with OWB just because the pants will hold things together. The other factor I mentioned was how tight you wear your belt. If you wear your belt looser you need a stiffer belt I've found to keep your pants up because they are riding more on your hips, also that division of the weight allows the gun to carry further around your waist which means one side isn't dragged down nearly as far.
So all of that said I've run into a few people who don't notice a difference in their particular method of carry between a gun belt and a normal belt. I think it might be a combination of body type, clothing, and tightness of their belts but I really don't have a good reason for it. Nearly all of the customers I talk to after the fact are amazed at the difference it made for them carrying, and I speak to nearly all my customers after the sale. Also a large number of them have been carrying for years without a real gun belt at least for civilian clothes(LEO's etc) and just can't believe the difference it made for them. So I don't have all the answers but that's what I've seen and been able to put together from that.
BLADE-TECH Reinforced Looper Gun Belt - Solid Color 1.5"-1.75" :: Belts :: Apparel, Belts & Multi-Media :: Blade-Tech Industries
And the gun/holster combos have been a Sig P220 with a Galco Royal Guard, a S&W M&P 45c with a BladeTech kydex IWB, and a Sig Pro 2022 in a Old Faithful hybrid (I have been trying all those combinations just to test this belt out... the M&P is the EDC). I don't find any of them particularly uncomfortable, I am just saying I don't notice a difference with the new belt over the regular old belt I was wearing in an IWB rig. I did try the 220 in an OWB holster I have and I see the difference there for sure.