Conquerer conquering too much
Conquerer simply is just too strong compared to any other mastery, it's been getting numbers of upwards of 500 extra damage per fight against a single opponent, gives ad and true damage which early levels outrank every other mastery possible for AA champions in the jungle and in top lane. I think it has been allowing people just to face role against fighters and bruisers who simply can't build the mastery. I think some nerfs would suit it and put it possible on the same level as masteries.