1st: Prof and other Magic Users are BASICALLY a support type. And also have DEFENSIVE SKILLS built only to it. Learn to use them. Cause even up to now im learning how to use skills and put them into action in right situations.
2nd: Theres so many things u can do when people go on Gtb, Like strip/Stave/Ifrit Rings/Get Melee Friends to kill.
3rd: If u damage low as ray said, u probably got a problem on ur gears and build. even legendary and knight set equips can deal a decent 13k-18k damage. (ive tried it as i started with those items as prof till now.) or people are on redux. but as far as i can see. no redux type can kill u unless its a taroter or u dont have seed.
4th: And fro almost nerfed many things. GTB case would be a long issue and argue + inputs before any changes would come again as i see it. But still does not guarantee it.
5th: Why would you use Wizard on MVP hunting, rather use sniper/champ. But yeah u can use it but not as viable as the other jobs. even with vesper card+3 kiels is not enough for a wiz. since its bolts is lower than a prof.
6th: See wizards and profs inside woe/gvg/br on how can they be very useful and vital. and specially wizards can own multiple enemies at once since during this fights they cant gtb always. and if ur refering on 1v1 PVP. refer to 1st-3rd.