Comparison for Magicians ' MP (Pre Big Bang and Post Big Bang)

So my Mage after big bang has higher MP because the 4 INT Masked Gentleman 's hat helped him ?

No, if you applied the 20% extra MP from MP Boost to the old mage, you would have 2259 MP at level 30. It has 20 more theoretical MP because it levelled up with more INT and your gear on your post-BB mage doesn't add enough int to make up for the luk you added.