Maybe you didn't notice that the lower damage one also has porportionately lower attack delay, thus meaning you attack faster with it?
i think in the first place they were not going to give certain classes any gear from certain GC's, so that all the GC's had a sense of individuality. but then they thought this might make one GC more popular, so they decided to allow any class get gear from any GC. but at the same time they had to think of a way to keep GC's individual and that is why the gear is slightly different.
(its this sense of being different that installs loyalty and pride in your GC)
go maelstrom
well if I assume the current delay and damage calculation wasn't change, that tiny delay improvement wasn't giving any advantage.
I made 2 double materia (tier III + tier III) attached axe to test with friend. one of them is str + str (+22str); the other is str + att (+11str +20att).
attached axe is Demilune Bhuj dmg:141 delay:4 Attack Power : +6, Crit Rate : +12
I'm using my Ifrit's Battleaxe dmg:171 delay:4.3 Fire Resistance : +15, Attack Power : +20, Fire Damage : +1
test object is L50 that lizard pug.
on normal attack, my Ifrit's Battleaxe out dmg double materia-ed Demilune Bhuj by 20-40 (kind of forget exact amount).
On Storm's path, Ifrit's win by 100-200.
This is vs doubled materia attached item, and the low base dmg weapon is already lose horribly.
(by the way, if you are curious... The str + att is way better than str+str XD on both normal att and ws dmg)
I also don't think the damage calculation can be simply put as (weapon dmg/ delay). Just single WS dmg lose already hard to make up.