I wouldn't condone the strategy of having two Axe wielding people in your party, mainly because the amount of attack points it differs from is ridiculous and is not reliable enough in battle sometimes. I like to traditionally set Basch as my Axe guy, but Balthier wields poles/spears.
I remember saying to myself that Tyrant was the easiest and worst boss ever. Maybe it was because Vaan was around level 55 and the others were 45.

But anyway, just bash attacks down on him and level up a bit more so that you're on the same levels as the fiends in that area. Every time he uses Graviga, just make sure you heal up and revive characters.