I suppose.
If you're wearing a good rig, when things really do need adjusting, it can be done by taking hold of the belt, instead of the holster or the gun.
But if you're having to adjust things on a regular basis, something needs changing/improvement. If the holster fits the gun and is good quality, and the belt is the right width for the holster loops/slots and is good quality, suitable for supporting the weight of the gun and holster and fits the person too, then things shouldn't be shifting around very much, if at all. If a person tries to carry a really heavy or large gun, then the whole job gets a lot harder and it could be taken to the point that it might not be possible. If a person tries to carry in a holster that isn't a good fit for the gun or with a flimsy belt that is much thinner in width than the holster loops, then they will be adjusting much more than they should. If they carry without a holster with the gun in their waistband, they're going to be adjusting it all the time--likely with an occasional wild grab to catch it when it slips.
My main carry rig is a horsehide belt that fits me well, is very stiff, and is a very tight fit for the holster loops on my carry holster. The holster is positioned so the belt loops, which are only just a hair over half an inch apart, are on either side of a pants belt loop so they can only slide a fraction of an inch in either direction--and they are so tight on the belt that once the loops are snapped it takes a serious effort to get the holster to slide on the belt at all. The holster is good quality hard leather made specifically to fit the model of gun that I carry. The gun can't shift in the holster, the holster can't shift on the belt, and the belt isn't going to shift very much on me. If I do need to make some kind of an adjustment--which is not at all common, I can do it by taking hold of the belt--there's never any need to touch the gun or the holster.