What am I missing in this formula?
From what I can see and remember, the logical way of interpreting that attack formula is:
(Attack Stat * (1+trait bonuses) + extra bonuses from spellcards/terrain/special mission situation) * Weapon Base Damage
where 'trait bonuses' are in percentages, so Attacker Lv 1 = +10%
Is there a reason that the enemy AI favors attacking Youmu over attacking marisa, when it seems more effective to attack marisa or even Chen. Why did all 8 monsters attack youmu. The fireflies decided to commit suicide. The AI should know that youmu cuts fireflies in one hit.
Check the AI decision making link. They don't think about their own safety (which is about right - we don't want cowardly mooks). Weighted decision means proximity plays a large part. Also note that the current AI is not taught to assess if the target is extremely likely to dodge.
-------------
So, I will assume that all Spells have base power of 2 and base shield of 1. Let's output some numbers for Marisa combat in that mission:
First, the Real-type tank check... she'll only get an 8% dodge chance against most enemies there (on neutral terrain) so no, she cannot rely on dodging. All the enemies have an attack stat of 8 whether it be STR or MGC (except for the tree and the boss). Assuming no bonuses, that's 16 attack power and so Marisa eats 11 or 13 damage from a single attack assuming neutral spell alignment matchups. Clearly, putting her at the front is suicidal. Her job would then be mopping up whatever the tanks failed to kill on their counter attacks the previous enemy phase - she does around half damage when she hits a fairy or tree and if Youmu has done her job then that should be a killing blow.
That's not broken from my perspective. If anything, the only thing she needs is higher agility so she has a reasonable chance (like... 30~50%) at evasion - maybe even give Flying an agility boost. Balance can be sorted later though, so I don't worry about it at this stage.