I'm not sure I like this at all:

If exp is based only on claiming, then this claiming system will be nothing more than an easily exploitable powerleveling tool.
However, if exp is based on damage to the mob, then the claiming system can be used to grief other players by high levels who go around killing mobs that others are engaged in fighting.

a /blockaid addition might fix this issue though.... Personally, I would rather they made this new claiming system an opt-in feature by creating a FFXI-like /HELP option, except the original claiming PT/Player can still get exp and items.