Didn't check the forum this weekend, but thank you Verda for correcting these people who are bad at math.
MDB does not affect MAB in any way different from how it affects the entire magic damage term, BPdmg included. Those who are laughing at me for posting math they don't understand, check your ego.
Here's a dead simple example. Let's say you have a mob with 50 MDB, and you hit it with a nuke that has 1000 base damage. If what you claim is true, then 100 BPdmg should give you more of a boost than 100 MAB, because the mob has 50 MDB, right?
With 0 MAB, 100 BPdmg, you will deal 1000 * (100/150) * (1+1) = 1333 damage.
With 100 MAB, 0 BPdmg, you will deal 1000 * (200/150) * (1+0) = 1333 damage.
Exactly the same. MDB doesn't make your MAB less valuable at all.
I'm fairly certain this is even true in the case of things like GEO debuffs which reduce enemy MDB below the base value, though I admit I could be wrong on that count.
How magic damage works.
MDB of the target directly weakens your MAB.
They're a ratio.
It's literally third grade level math.
Do you not recall how denominators work?
They're not a ratio, they're multipliers and divisors. Do you not recall how ratios work? It doesn't even make sense to call a term of a formula a "ratio".
As Verda pointed out with order of operations, those terms can be moved around without affecting the formula. Dividing the MAB term by MDB is no different from dividing the entire formula by MDB, because there is no addition/subtraction going on in the magic damage formula.
This is a 100% completely accurate magic damage formula as well:
Damage Dealt = (D × MTDR × Staff × Affinity × SDT × Resist × MB × MBB × Day & Weather × MAB × TMDA × Potency Multipliers)/MDB