Bond strength of carbon compounds

I read online that C=O is more stronger than C=N and the reason behind this was, 'Since bond between C and O is more polar hence it will have a slightly higher ionic nature than C and N. As we know ionic bonds are stronger than covalent bond hence C=O bond is stronger.' 
Then I tried to find the bond strenght between C-O and C-N by applying the same logic but the result turned out to be the opposite of what I had calculated. According to factual data C-N is stronger than C-O. Can anyone please explain me what's wrong in my reasoning and whether it's right or not.


