pre-shamballa: he's twice Ed's size, can't feel pain or fatigue and has the advantage of his brother loving him way too much to pull the only cheap trick that would work (water or aiming for the blood seal). Worst case scenario, all Al has to do is wait for Ed to get tired...
post-shamballa: Al's the only one with alchemy. Alchemy wins against clockwork arm.
More people need to recognize the awesomeness that is Al.