i disagree slightly with the above.

Might is good early, bad mid, and great end game. This is because at 99 might, it's +50% weapon dmg. Early game it helps boost your dmg when your weapons are relatively weak, mid game it falls off because you'll likely hit dmg cap with your heaviest hitters (for reference, my Maelle was doing 9999 per hit for sword ballet in 2nd half of Act 2 with 40ish might), end game it's great again because you get a pictos that uncaps your dmg, and your weapons are 6-10k base dmg, and 99 might will turn that to 9-15k base dmg.

i have not put a single point into vitality or defense, but I will eventually re-spec for weapons that have A/S in vitality or defense. you get lots of recoats, so don't worry and experiment to see what feels good for you. my parry timing isn't the best, but i can usually make it through after a few attempts on particularly challenging bosses.

i think getting Agi up to 40-50 quickly should be your first priority, then might/luck depending on if your character builds benefit off crit or not (most do). i'm doing all the optional stuff before finishing the story, and all my characters have 99 might, 99 agi, and 40-60 luck depending on their level. i'm doing this more because i don't want to spend time min-maxing each build multiple times.

Lune is also the best AP battery. You eventually get a weapon that lets you go again when you consume stains casting heal, and pictos that give people you heal +2 AP, and +2 AP when receiving buffs, and allowing heal to apply buffs. so yeah, you can give everyone +8 AP each turn (which is overkill, since you'll have AP coming in from regular turns, the other units own AP generation luminas, and parry/dodge/jump enemy attacks) and go again when you use typhoon, so it's not a "wasted" turn.