Surely you can safely add 25 hp of NO2 to a 421, which would then give it more hp than your Cheetah? I'm not questioning that your motor runs great or that you beat the 421 on the spray.
I think the reason a lot if us pick the Cub over a Cheetah is most of us have never seen a real good running Cheetah. I used to have what I thought was a good running 14 Mil Cheetah that was #1 qualifier in the 0-650 class at Gilbert 2 or 3 years in a row, several years ago. My 10 mil Cub has run those same times, albeit in a better chassis.