Quote Originally Posted by Psyren View Post
A simpler way to restrict caster armor (if that's your goal) is to cap them out at one step up from baseline. So no matter what a wizard or sorcerer multiclasses with, the most you can cast their spells in is Light Armor; the most a Bard or Warlock can multiclass up to is Medium Armor, and Clerics/Druids/Rangers can multiclass up to Heavy. Subclasses would get to override this as normal.
So a Fighter that multi-classes into a Wizard loses 2 levels of armor prof? And what about shield prof? Shields will usually be the more problematic part for casters not armor.

The real answer is just making armor prof harder to get, and increasing the Str requirements for medium and heavy armor so they require at least some attribute investment to function fully. Of course the first of those is easier said than done because it requires changing the class benefits, and a reason to start in a caster class over a class with lots of profs (assuming the profs would be beneficial).