About the bladestorm thing: I leveled primarily with BGs from 65-69 as arms to get a feel for it. Bladestorm did incredible damage, like I really did feel like I could wipe a team with it and that was just with whatever gear I got while leveling.Their damage is fairly similar. If you have a pocket healer I'd suggest you pick the spec you play best/have most fun with.
Arms has the pleasure of anti-heal which makes healers much easier.
Fury has the pleasure of self-sustain which makes solo games more fun.
All being said - at 69 you get bladestorm for Arms which adds a huge part of his kit to the game. If you twink properly you could potentially wipe out a whole team with that button.