I think the point being made is that most places would like a DMR specced airsoft gun to look like a real world DMR. E.g. a M14, HK417, SR25, Dragunov, G3, etc. There's no real world situation where an infantry unit's designated marksmen have been issued the MP5, because it's very much a close range gun. Going by your logic it would be perfectly acceptable for me to get a pistol shooting at 400FPS and claim it's a DMR because it's semi auto only.