Most classes have at least one skill to keep leveling late in the game that requires a higher job level. Magus doesn't have this, wich makes it less rewarding te level past 180 ish compared to most classes. A quick look at the leaderbord and you'll see there aren't many 180+ magus players. I think this partially why.

It would sugest a skill that makes it worthwhile so either 2h axe training (like WK) or Support of Gust (mage support class afterall).

See examples below:

Magus meanwhile has nothing: