Because debaters who are arguing for western made fictionals characters need to compensate for the relatively less stellar cartoon animations compare to DBZ and anime in general.
If you look at early western cartoons like x-men, superman the animated series, batman the animated series... fight are pretty much generic brawls that you see on a typical american backstreets. They are slow and graceless (but compartively fluid and well animated).
Japanese animes, because of cost cutting, pretty much skip much of the animations but created a distinctive anmation style that utlizes blurs and ultra-fast movements that creates an illusion of speed, bad-assery, and chaotic destruction.
I mean really if you compare the fight between Gokou and Piccolo against Raditz (hypersonic punches, mountain busting explosions, amputated extremities, blood and gore) with that of Superman against Darkseid (just a bunch of muscle bound spandex characters beating each other up barfight style), for example, even kids will tell you that Goku would easily creamed both Superman and Darkseid.
Hence western character debaters need to compensate by down dumbing the DBZ feats.