I feel like Titan weapons were originally intended to be a higher item level, but then things were adjusted.

The reason I say this is because the Relic weapon, in beta, was item level 95. I remember very distinctly because I was super confused by it saying "Lv. 95" in my WHM equip log. Then it got downgraded to item level 80, presumably to 'make room' for the +1 version that may or may not have been 'rushed'.

Ifrit: 60
Garuda: 70
Titan: 70 (Maybe it was meant to be 80. Originally. Before the relic iLevel got downgraded to make room for the relic+1.)

Now it seems silly and weird. I personally think the Titan weapons are super ugly. Perhaps if they add in some sort of aesthetic feature, people will actually want these weapons.