It could simply be because hunters are probably the class that would allow players to snowball the best when on kill streaks, thus more skilled players who are easily capable of netting continuous kills benefit a lot from using hunter. Gunslinger's Trance and Chain of Woe allow hunters to have an even easier time getting a kill after going on a kill streak. The other classes possess no such mechanic. This doesn't necessarily mean that hunters are OP though. Chain of Woe and Gunslingers Trance would be almost useless for the majority of players that die before they can get successive kills for the abilities to kick in. I'll admit that the persistent nature of hunter supers makes them better for engaging multiple enemies that aren't grouped up closely, which seems to be the case most of the time, but their grenades and melee abilities are lacklustre. Again, the better players would be able to take advantage of the supers more as they'd build up their super faster with their constant kills. The average player would end up with inferior melee abilities and grenades for most of the match and occasionally getting the chance to use their super. Also, Hunters' stat boosting perks are skewed towards agility, which is actually one of the most useless stats for a hunter. Or for any class in general due to the extremely small boosts.