"Full-time Employment is a Loophole in the Law to Make Wages Lower"?
If one is salaried, one doesn't usually get paid overtime. Aoba, presumably, is salaried, so like many full-time workers, she won't get overtime. 

However as a part-time/temp worker, Nene would likely get overtime which is why she could end up earning more than Aoba.

As a general example, videogame programmers work longer hours for less pay compared to programmers in more "soulless" industries.

They usually have relatively more passion for their work than those from most other industries. Unfortunately, there are companies who are happy to exploit that to drive wages down.