NIN isn't really difficult but it has the highest APM (actions-per-minute) of any job and you're going to be shoving a bunch of things in your 15s Trick Attack/20s Mug window and for the rest of the time you're basically just hitting 1-2-3 and dumping Ninki outside of that. If you don't like busy jobs with tight windows it's probably not for you, but it's also not "more work for less reward" because it is the highest DPS job in the game at the moment.