Nargott
I always thought they stacked, one and the other.
But that doesn't matter – you can't push a hero further than 30% of their Action Points (with skillful spellcasting), and it will push them exactly 30%, and Distraction itself will do that.
Mass casting in this mod will also push to 0% Action Points, not 50% (meaning it will take up the hero's entire turn). So, Distraction is a counter to Spellcasting, and nothing more.
Technically, as far as I remember, Stun is capable of pushing a hero into negative Action Points, but this is a temporary bug – any negative position on the Action Points is reset when any unit's turn begins.
I imagine it something like this: you choose a Light specialization, and within that Light specialization, you can also upgrade to a full Chaos specialization, or other things from Light and Chaos. The same with Darkness and Summoning.
No, the decision was made to abandon skill-based dampening altogether. For the same reason of redundancy: the power of a spell is weakened through Weakness, and there is already a perk for that (and a powerful one – the penalty will be 50% to spellcasting).
So, all that remains of the actual dampening is dampening perks.
I absolutely don't understand why you would invest more than a couple of perks in countering something specific (which each school of magic is individually). And together with the native skill-based dampening mechanic, that's how it worked – the player invested up to 6 (!!!) perks just to ban 1 school.
The closest example of a specific counter is the counter to archers. There are 2 perks: one is Dodge (-30% ranged damage) from Defense, the second is Mist Veil (-30% initiative) from Logistics. The player can invest in one of them (if they are worried), or invest in both (if they are 100% sure that there will be many archers). In this case, with just 2 perks, they will deal with enemy archers with 70% damage and 70% initiative, so their influence on the battle per unit of time is already reduced by half. Why counter even more? Any specific counter of more than 1-2 perks is redundant.