While Million's explanation is good, I'd like to try my own phrasing:
In this context, setting up your character's armor by 'the meta' would basically mean picking the armor with the best stats, that maybe synergize with each other and/or the playstyle/class build that is the most overpowered, most broken.
You could maybe call that 'optimizing the fun out of the game'.
What this person, OP, is saying is... nah, I'm just gonna pick the armor/clothes I think look the best, knowing that will make things harder for me than just choosing the 'optimal' armor, and I'll either git gud at the game, or die trying.
Its... kind of like how DBZ characters wear weighted clothes.
Its an intentional, chosen handicap, in a gameplay mechanics sense, that makes things more difficult, so training / playing the game is harder... but if you can handle it, you're probably going to be better at the game.