Although I agree with you 100% and I also one of the guys that said only one group can claim a mob at any time, but still I think most of the people wanted this because of the RMT, like what happened in FFXI.
RMT usually never outnumber real players but they camp an NM 24/7, and even if they outnumber players, you see them competing against each other.
I know this option will destroy small group's chances of claiming NM's, but they still can do that in dungeons.