Yes there is an increase in DPS, like i said, but without adding 10 more STR you're still gonna be pretty damn close DMG-wise to the giantsgall, which is why it's better to have the giantsgall axe with enmity. I never said there is a magical bonus. The bonus comes from more STR/VIT, that's it, but 10 STR is fairly significant. If you do go out and adjust your gear for the higher stat caps, garuda's axe will be better enmity-wise in addition to DMG output. Then there is the case of pure DPS, (ie., not tanking) in that case garuda's axe is always better than a giantsgall axe.
