Actually, for me, Tyrant was incredibly easy, which surprised me somewhat, given how difficult he's made out to be here. The gambits weren't even that complicated. If you have at least one tank that uses melee weapons, and one that uses ranged weapons, you shouldn't have much of a problem. 
 
Tanks: 
[Foe: any > Attack] 
 
(Yes, it's really that simple) 
 
Here's the important bit: your casters. 
 
Casters: 
[MELEE TANK > Decoy] 
[Foe: any > Dispel] 
[Ally: any > Protect] 
[Ally HP = 60% Curaga] 
 
Why 60%? Becuase one of Tyrant's attacks is basically a beefed up Gravija spell that ignores Reflect and other armor-boosts. But, as far as I can tell, it has a small radius. The move, by its nature, damages your characters by 50% of their Max HP. Thus, you don't want to let your decoy's HP drop that low. Ever. 
 
During the actual battle, let Tyrant focus on your melee tank. Your ranged tank will more than likely back away from the target before firing, as that's what their AI is programmed to do. Your party leader should be your caster, whom you should keep at a distance from your tanks using the control stick. 
 
Then, just let your tanks hack away, while your caster keeps the decoy healthy. If one caster runs out of HP, switch in another. If it looks like the decoy's HP is below 50%, have your ranged tank toss in a few Hi-Potions. 
 
Now, there is one caveat here: my characters were around level 45, rather than 40. Still, I think that setting a high percentage for your Curaga should make this relatively easy.