Putting on a bench shirt or knee wraps or a squat suit doesn't make one stronger. No. But it provides a mechanical advantage, immediately and without question. And with practice, guys can maximize that mechanical advantage and move way more weight. There's a reason why all the geared records are higher than the raw ones, and it's not that the athletes are necessarily stronger.
Of course, there are some guys who do lift both in gear and raw. Joe Mazza comes to mind. He at one time held records in both raw and geared bench press at 165-170 or so. IIRC he benched 485 raw and 705 with a shirt.
Yes, the shirt gave him 220 pounds.
The thing to understand in powerlifting is that there's protective equipment (like a belt, wrist wraps, knee sleeves, shoes) and there's assistive equipment, as previously mentioned. The protective stuff doesn't by design add pounds to your lifts. It makes them safer.
Assistive gear, by design, adds pounds to your lift via mechanical advantage. Or, like wrist straps for deadlifting, allows you to complete a lift you otherwise couldn't.
Why can't a person be expected to instantly get hundreds of more pounds the second they put on a bench shirt? Because it takes a little time to get used to the equipment.
I was a pole vaulter in high school. If I handed a high jumper the pole and told him he could instantly go over a bar ten feet higher than he's ever gone over before, I'd be lying. But the mechanical advantage of that pole does allow it, once he practices for a while.
Just as you can't compare a pole vault with a high jump apples to apples, you can't compare a geared lift to a raw lift without mentioning the equipment.
But don't get confused. Both a high jumper and a pole vaulter wear shoes to protect their feet and grip the track. That's universal equipment, like a belt in both raw and geared lifting, meant for safely. Taking away a belt may cost pounds due to lost stability and intrabdominal pressure, but a belt isn't considered assistive.
Hope this clears things up a bit.