I wish people would stop trying to suggest that traders should get AoE debuffs to make up for bad effectiveness. I also wish both players and especially FC would stop trying to balance AO around team play. As in, wanting people to be in a team or else suck.
First of all, AO does not support balanced team play. There's not enough people for this AND there are too many professions for this. Most PvP situations does not involve having two teams of 6 perfectly mesh together in a team vs team fight. This just never happens so why would anyone balance for that scenario? Being ineffective in PvP when you don't have a team to back you up is a sure fire way to have people get frustrated, since most of your time is not spent in such a fairytale scenario.
And btw, balancing professions for teaming scenarios is just a surefire way of shooting yourself in the foot. If you balance professions for solo play and add some minor team buffs then you will have team balance as well automatically. If you balance professions for team play you will have frustrated soloers (AND frustrating low numbers pvp as team-balance wont come into affect until you got a small raid on each side). You will have rock/paper/scissor encounters where you will either steamroll someone or get steamrolled and neither of these are fun. People will feel forced to team and if the right mix of professions isn't around, the other side will steamroll you. Let people team because they want to work together, not because they SHOULD or HAVE TO. That's the absolute last thing you should ever do to a low population game like AO.
Also, why would you want AoE debuffs and bad single debuffs and bad defenses when you repeatedly will find yourself fighting someone alone or WANT to fight someone alone and all you can say is "if you had 5 more friends with you and I had 5 more friends with me as well, I'd be a little bit annoying, so even though you alphaed me now, just keep that in mind please!"
If you want people to have fun all the time, then balance professions around solo play and have team buffs be minor. That way you can be effective no matter what the scenario is, when you team up it wont matter so much what professions you have (like engie being a must-have and such). There wont be rock-paper-scissor encounters ALL the time. If you are unable to be part of a perfect team, then that wont be such a big deal.
If you want people to be frustrated, go ahead and balance things for team play
I'm sure some of you (hey Obtena

) are thinking stuff like "Well, FC's is going for a different kind of balance where not every class is great for PVP by themselves and that if you want to do nothing but PvP, you should roll a different profession. If you think trader will only be useful in specific scenarios then just bring out your trader for those scenarios and use a different profession the rest of the time".
2. No MMO should be designed around having more than 1 character. "Wait a sec, let me relog to my other character" should never be the go-to-phrase in a MMO. If you can't have enough fun with your main then the game isn't finished yet and needs to be worked on some more.