I don't know if it's too early to start theory crafting or not but I'm going to anyway.
While running dungeons I noticed that other tanks had 100-150 HP more than my Duskwight Elzen. I realize now that Vitality directly increases your max HP, and that Duskwights have less base VIT than most races. I have been putting all of my bonus points into Strength at level ups instead of Vitality like everyone else because I know that it increases mitigation and indirectly enmity. The damage reduction seemed noticeable to me as it seemed like I didn't take quite as much damage as other tanks.
What I was thinking is that perhaps GLA is meant to be more of a mitigation tank while MAR is meant to be an HP tank. In other games Mitigation has always been better than just stacking HP except in cases where massive burst damage is caused. I suppose high HP would also be good for Caster enemies until Resistance gear is viable.
I know that the end result will be some sort of balance between the stats, but as Materia use becomes more commonplace this will definitely be something to consider. I for one will probably lean more toward Strength than Vitality.
Oh poo and there is Mind/Piety too.. whichever increases magic resistance... fun fun XD.