A .22 or 9mm is not necessarily easier to hit a target than a .45 1911 because of its caliber, unless the shooter has a flinch that anticipates later recoil after the bullet has left the barrel.
Larger caliber pistols simply take more time to regain a sight picture, and are harder physically on your arms and shoulders after a full day of shooting due to harder recoil. This isn't that much of a factor in this fun little game, where time isn't an issue and its us guys that mainly shoot the larger guns.
In sports such as IPSC, power is rewarded (except for Production) because time is an issue, and your score is affected by it. The power affects your ability to shoot accurately quickly so much, that everyone I know who competes loads their own ammo to just safely satisfy the requirements of the "Power Factor" they decide to shoot with. We do the same, since my wife and I are also into IPSC on a regional level.
This is just a fun informal game we do with friends that gives us a break from the pressure of having to "Stand by" before the shot timer beeps.