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On the contrary, I've heard long hair actually makes you go bald faster.
Literal
Rather, long-hair [gen-of-side-のほう] [subject-が] bald-easily [quotative-って] heard [ぞ].
A counter-intuitive claim. むしろ ('rather, on the contrary') is a discourse marker that pivots to an opposite claim. ロン毛 is slang for long hair — ロン from 'long' + 毛 ('hair'). 禿げやすい is the compound 禿げる ('go bald') + ~やすい ('easy to / tends to'). って is casual quotative. 聞いたぞ ('I heard, I'm telling you') with the masculine assertive ぞ. Typical of a friend sharing a curious fact with assertiveness.