Unless Im mistaken, experience is earned by damage done and then is divided by the whole group. Ill try to give a simple example involving a tank, a healer and a wizard.
So lets say the tank does his job and puts on a shield, protecting the squishies and soaking up huge amounts of damage. The healer does his job and buffs, removes ailments and heals everyone who needs healing (with the occasional DoT or debuff thrown in). Then we have the wizard, who only has one job and that is to do crazy damage.
Now lets say they all work together and earn a kill thats worth 2000 exp. In this case the tank will have done 1000 damage total. The healer will have done 500 damage. And the wizard will have done 5,000 damage. Since the tank and healer are grouped they split the exp. They both get 230 exp each. The wizard however, since he was solo, gets 1540 exp. In what world do you live in that you would consider this fair? How could you possibly rationalize the situation so that the wizard is not leeching off the tank and healer?
Without the tank no one would have gotten protected. The wizard would die in five seconds and the healer might be able to run away. Zero exp for everyone. Without the healer, no one would have been healed. The wizard would die in four seconds. The tank would probably die too with very low chance of escaping. Zero exp for everyone. Without the wizard, it would be a stalemate. Not enough dps to get a kill, but enough protection/healing to stay alive. Again, zero exp for everyone.
I think its safe to say that the tank, healer and wizard are all needed equally (give or take). Yet you somehow think the wizard deserves a 650% exp bonus...
because no that wizard is not receiveing any group benifits, he doesn't get buffs, ehalers wont notice him and heal, tanks arnt going to protect him. You pretty much give up all luxuries of a group for the chance to earn more xp.