Persuasion checks are not spells. Sounds to me like some DMs let a success at Persuade have too great of an effect.
Back on the topic of min/maxing and powergaming...
Min/maxing simply means that you focus completely on one things, at the expense of everything else. So you're awesome at hitting things with your great sword, and not much good at anything else. So all the DM has to do (assuming he wants to keep things balanced for the rest of the group) is make sure there are lots of situations where hitting things with swords is not the answer. And some things where hitting things with swords is the answer, so that one character has fun.
Then there's exploitation of poor game design through specific builds. Shouldn't that be solvable through simply talking to players at the beginning of the campaign: "Ok, look guys, I know GWM/Polearm Master does tons of damage, but we've seen that character a bunch of times already. Can we try something else? I'll tell you upfront that there are no magic polearms in this campaign..."