Almost every tree has a passive that grants you a bonus for stacking abilities of the same tree, like sorc, that gives you 2% spell dmg for each sorc ability slotted, Mages guild gives you 2% max magicka and magicka recovery for every ability slotted.

The same doesn't happen with Destro passives, there's only "enhancement" focused passives

I was thinking about change how Penetrating Magic works, the passive that "allows your Destruction Staff spells to ignore 5%/10% of an enemy's Spell Resistance".

Maybe this passive should give a flat value of Spell penetration + another flat (smaller) value for each destro ability slotted. This will benefit builds that doesn't slot destro abilities, while also giving a bonus to builds that goes for 1 or more destro abilities.

This flat value should be like, 1000 spell penetration + 750 for each ability slotted. Or something like that, not sure about the exact number, but it shouldn't be something behind the current Penetrating Magic, but it also should goes further from the current Penetrating Magic for builds that slots several destro abilities.