Yeah, even powerlevels manage to get to 30 or 40 or even 50 without doing jack on their own, they're going to eventually run up into a wall where higher-level characters can't help them XP anymore. Then they'll be forced to party and nobody else is going to want them, because they'll suck so bad at their job. Also, I imagine while they're so busy xping like madmen they'll forget to go out and farm, meaning they'll be stuck with gimped equipment all the time. I don't like powerlevelling, either, but I don't think it'll become a big problem as it can be capped at some point and then those people are screwed. Its a self-defeating ideaology. A *little* PLing doesn't bother me too much, as long as the player has experienced the hard way first (like they've been stuck at level 15 in Valkurm for a week and their only stumbling block is the people around them, for instance). Its really the people that abuse the system that piss me off.
Fish-botting sucks, too, but thankfully its really the only true means of cheating in the game so far. FFXI has enough non-cheatable content that its rediculous. You'll never be able to tackle higher-level stuff and missions and crap through cheating.