Okay, in hindsight I admit that was something of an exaggeration on my part, so I'm sorry for wording it like that. But the point is, fighting a higher level mob does not give extra exp you wouldn't otherwise get for fighting an enemy around your own level, which is how exp parties were viable in the first place in FFXI.

Really you're just better off doing a levequest or a FATE than bothering fighting random enemies, as the FATEs/leves give you an exp boost for doing it - it's not the individual enemies that are the point of fighting but the exp bonus at the end.