And what's make you think they are equally strong as SS2? They have never fought each other in that form, and the instance I refer is what were mentioned above, in the BoG and GB Arcs. I mean if, what makes Trunks SS2 "special" is pushing his form, why wouldn't apply to Vegeta? A difference from Goku is that he doesn't have a SS3 form, so he has no choise.
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