I've never played FFXI so I can't really comment on that except to say that it's my understanding that mobs respawn WAY faster in WoW than in that. So while it sucks to have your camp cleared on you, the mobs will be back shortly.
As for the rest - I'm not exactly sure what's going on. Are the other people killing stuff you're not actively fighting? If so - again, an annoyance but like I said above, if there are a lot of people clearing stuff fast then the respawns are generally equally as fast. Another option there would be to whipser that person (type /w playername) or just in say and ask if they want to group instead of fighting for the mobs.