To be fair, the reason i think the author did that is because innumerable plot holes would be formed with multiple 'regressor' skills existing, it could've very well destroyed the fabric of space itself with contradictory actions, lol.
I like both Asura and Reaper. They both do a good job and both have series I read. I'm not sure why they're fighting like this, I wish they would work some shit out between them but I mean I'm gonna read these chapters tho... Still, make love not war.