DTR population stats:
Class breakdown: 34% hunter, 34% warlock, 32% Titan.
Top 100 Class Breakdown (PvP): 44% Hunter, 29% warlock, 27% titan
Top 10,000: 37% hunter 33% warlock 30% Titan
Im not sure how you collected your stats, because DTR has these stats available for you to view directly without any ambiguity over what stats are classed as "top 100".
Anyone in top 100 can easily play any class, their skill doesn't lie in using a certain toolset. Sure they will have a preferred class, but they would dominate on any class.
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But they dominate even more with hunter. That's why they use it.