Why put a category cap at all?
With players now having many (if not all) jobs near cap, each job requires different skills/attributes. Since people get a crazy amount of experience in aby in all sorts of ways let us use it. Let us cap all magic skills (since each type of mage needs different types of magic) and weapon skills.
No matter how high you put the maximum merits stored, that maximum will be reached in days (2 weeks tops for occasionnal players) and then we will be back to the same old story of tossing all our experience gained into the toilet.