I have shot 25 yards benchrest with an air rifle and achieved a score of 100.
There are many shooters regularly scoring tons in 25 yard benchrest league competitions, but, there are very few pistol shooters at club level who achieve 100 ex 100 regularly, especially at 20 yards.

The reason why pistol targets are inward scoring and rifle outward is because of the difference in the degree of difficulty.

I do agree with you though, it is much more difficult to score 100 on the 25 yards benchrest target with an air rifle than with a .22 rimfire. With an air rifle your technique must be spot on, probably due to the lock time (the time the pellet/bullet is in the barrel).