Mathematical balance of A-skill (late anwser to Wyatt)

This is a post to anwser & explain the theorical balance between all the A-skill, following an unanwsered question from Wyatt.

https://fireemblem.gamepress.gg/q-a/anti-fury-skill

==================The Question :
"Anti-Fury" skill

I wonder if there could be some A-skills
Like "Fury", but not Fury

[All stats - 3],
but heal HP after after damage. (Complete opposite of Fury)

[All stats - 3],
[-1 cooldown] after damage (great with Galeforce and Miracle),

[All stats - 3],
When HP ≤ 25%, [All stats + 7], (High risk High return)

[All stats - 3],
After damage, enemy is inflicted with [All stats - 6]
{Better as a B-skill)

==================The Answer :

The way A-skills work is very mathematical :

Basic A-skill = 3 stat points (except for HP=5).
In exemple, Def+3.

Now you add a condition that halves its occurrence/potential, so you can double it.
In exemple, earth boost 3, if you put it on EVERY hero in the rooster, it will be like 2 side of a Spectrum where it's good to best on one side and bad to worst on the other, so it's 1/2 good in average.
==> So it's logical that it doubles the reward (6def).

Now you add 2 conditions to the basic Def+3 :
In exemple, Distant Def :
-Only when you are attacked (so 1 phase out of 2) = which would result in a 6 stat boost reward (Def+6 when attacked, just the opposite of Armored Blow, Def+6 when attacking).
-Now you add a second condition : "only when the ennemy is a ranged hero" , it's halves the rooster in terms of offensive possibilities, the reward should be doubled again ! In exemple +12Def.

However it would be OP to have +12 points of one stat (i.e. 12Def or Res).for exemple ranged attack are mainly magical and melee attack are mainly physical, so a Close Def with 12Def would be too good , or Distant Def with 12Res.

INSTEAD they give you 6 Def AND 6 Res. (halved the occurrence, but doubled the possibiliies, to make it back to a balanced potential compared to other skills).

So that's how every skill has a balanced Potential=1 .
But that's the way some skills are used / combined with other abilities, that makes them way better than others.

For instance, Deathblow3 + Brave weapons, it doubles the potential of Deathblow3 without adding a condition, because Brave weapons and Deathblow3 share the same condition (initiation only effect).