So let's imagine that we're in team sports. Team captains have been picked. No one likes them, but everyone thinks everyone else likes them so no one says shit, and any arguments are quelled by the vigorous collective shaking of blender bottles.
They're picking their teams. Captain #1 (henceforth known as Bert) picks Winston the Wizard. Captain #2 (Ernie) picks Drew the Druid. Bert picks Clarence the Cleric. Ernie picks Sue the Summoner.
This keeps going on for a few minutes, and eventually, you're left with a group of 5-6 guys. Most of them are wearing knee socks and what can be best eloquated as men's running shorts using half the material one should use for a pair of men's running shorts. Less thigh next time, guys, especially when your stilts look like a mating pair of albino caterpillars at weird angles. Two of them are wearing FitBits, and just when you can't silently judge them any louder, you spot a sweatband.
That guy with the sweatband? That's Mikey the Monk. He's got a janky leg. He takes yoga on Thursdays, and he owns three shakeweights. He will never be picked first. Or second. Or third, fourth, fifth, sixth or probably even seventh. He's not at the bottom of the barrel -- unlike Klaud the Kineticist, at least he doesn't spit when he talks -- but still. You aren't sure what the intended function of his wristwraps is supposed to be in a game of soccer but you could live with it if they weren't covered in YinYang logos. You won't say anything, but you really wish Winston's brother Churchill would show up so you could have a second cleric instead.
Klaud gets picked next. He spits without even realizing he's spitting. He can kick the ball REALLY hard, but only one direction (directly sideways) and he gets winded fast. Sam the Sorcerer can kick it further, and more accurately, plus Sam wears UnderArmor shit but Klaud insists on tagging along to do his shit anyway. You glance nervously to the shivering little group of remaining choices. Richie the Rogue. Vick the Vigilante. Mikey's inbred cousin Vin the Vow of Poverty Monk. You make eye contact with the rest of the group and realize that they, too, are trying to find the least offensive way to sideline these guys. Everyone breaks for lemonade.
....
....
....THAT is what your GM banned. Mikey and Klaud. You can optimize the everloving SHIT out of either of those classes, clone them, make the clones fight the original to the death, clone the victor and repeat the process until you have a genetically perfect clone and then fuse it with panther blood and Brad Pitt's DNA and you still won't be able to touch Winston on his worst day.
Your GM is an idiot and I suggest you steer clear.