Leveling; build for survivability?

[Estellios]

If your tanks are dying that fast in anything that isn't Coil, they have garbage gear and you should probably ditch them.

Not only will more MND make your heals more efficient it makes your MP usage more efficient and boost your nukes while under cleric stance (which you should always be using while soloing anyway). It is fine to put some points into VIT, I have, but you shouldn't put them all into it.

Now melding VIT materia on your gear, IMO, is a much better idea because usually you will not be able to add more/much MND to it.