I think you're forgetting that you can keep the leg enchant without leatherworking. You can also bug it onto your legs via the trade window bug, but that's another story.
LW for the leg enchant then drop for JWC. 57 str is 125 AP, which is 75 AP more than the 50 bracer enchant. It adds some parry (which as DPS is moot). JWC nets 3*14 = 42 extra str, or 92 extra AP. You also get access to the JWC neck and associated trinkets (which for PvE aren't as good as BT/SWP/MgT trinkets.
But, is it worth that 17 extra AP?