First of all I never stated it is overpowered. I said it's decent the way it is. I don't think stalkers need such a huge advantage to completely remove the need for kiel cards while all other magic classes except for ninjas need kiels to do anything with their magic.
Stalkers charm is obvious to me. (Copy spells, strip, backslide, massive hp) Especially the strip is what makes them unique compared to the other 'magic type classes'.
Magic stalkers can do the exact same thing. The only thing that would be different is the weapon as the bow has little reductions as well.
Well then I'd recommend you guys to suggest something that stalkers will be able to do vs GTB. This topic's suggested change would not change a single thing towards their weakness and it would STILL not be "attractive" to change to a magic stalker build over the prof/wizzy or ninja. Even though magic ninjas do not have a single thing they can do vs gtb either, besides trying to survive. At least a stalker can outwait fcp and then easily kill his/her target.
Wearing those headgears would require you to add quite some agi no matter what build you are in. Dex or int. Either way it's not smart to wear only 2 kiels with a magic class full time. So if you'd replace the poring tower with fhelm. You'd be unfreezeable have max aspd with less than half the agi the redux bow stalker would have , have more hp and be able to spam perfectly fine. In exchange you lose 10% reduction which the extra hp and extra stats to vit instead of agi make up for.
In short : There are possibilities in boosting up magic stalkers. But I don't think this is the right way. Magic stalkers will still have the same problem with this suggestion implemented as they have now.