Are runes +'s stackable?

I have put 3 runes of minor swordsmanship into 3 different armor pieces for my warrior. However according to my hero's atrribute , he's at level 13 swordsmanship and but is actually at 12. Shouldn't my swordsmanship be at 15? I thought that it could be because level 13 is the cap (since I couldn't add anymore attribute points) , but I tried decreasing the skill but still only have the +1 bonus. Is there something wrong here.. or did I just wasted 2 swordsmanship runes?

Nope, runes do not stack. Only the highest one is counted

Think about it, if you could stack 3 minors to the same effect of a superior, only without the -hp, who would use a superior?

I would stack 3x sup and then 2x sup vigor and be GOD

It would be great to be able to raise my expertise from 16 to 20+ ... Just thinking about all the 10 energy attacks would be free and the 15's would only cost 2