Bronc - There are many now who feel there are too many, perhaps way too many categories already. Adding a major / minor power factor category, or divisions to all existing categories would just not be practical.
Back when things moved from pretty much just Modern and Traditional the powers than be chose to break out the ages, costumes, and shooting styles rather than power factor. With shooters from about 8 to more than 80 that seems to make sense.
Classic Cowboy is the only category with a caliber requirement other than just the basic minimums, but it doesn't have any power factor restrictions other than the minimums for all categories.
Grizz