Of all the suggested changes to armor, this is the idea which I agree with.
I think the ratio should be something between 66:33 and 75:25, and the damage hits. Any lower than 66% would make the effect of different attack types working better against different armor types almost irrelevant, and any higher than 75% would make the damage done to the opposing type too minimal to be much use. So maybe 70:30 is a good ratio.
IMO doesn't make much sense to a magic spell to do damage to Physical Armor,
Why not? The armor is tied right to the items themselves. Should plate mail be completely invulnerable to fire or electricity? Should a sword pass completely through a magical shield with no effect?
I don't see any particular lore reason why the respective armors must be completely invulnerable to the opposing type. We can just say that the armor is not completely efficient against the opposing type.
The armor system was created to prevent you doing CC to multiple enemies easily like in the first game. It's not perfect (make CC lot less appealing) but it do good job.
I agree with this, but that doesn't mean the system couldn't be tweaked a little. Right now a mixed party of 2 magic/2 physical attackers doesn't synergize well with each other because one armor type can be gone but the other teammates can't take advantage of that.