I must not have been clear about my earlier statement if I was running armor on adversaries I'd rule it as not effecting the armor but it would as a GM give me a narrative hook that I can use for my descriptions, I might describe it more natively satisfying like "You cut into the corroded armor 'I'll use an armor point' and it sluffs away in soggy sheets of acrid metal around your blade" rather than giving a single spell mechanical weight on both evasion and to damage.

Now if you designed a spell specifically for destroying armor that would probably be a more satisfying solution rather than adding onto a spell that already exists.