There is another thread in the forum with the same argument, just didn't have the proper tag:
http://forum.square-enix.com/ffxiv/t...lly-dissappear

The basic idea though is the same. The claiming system shouldn't be changed, at least not for the regular mobs. It should only be modified to allow a party to fight several groups, rather than only one (which is the problem that happens at Behest).
As for Large Scale Events, if they are instanced, monsters could be allowed to be fought by anyone who is part of the instance.