Great idea, what are you mad at more options to level up?
Also as PVP you can change jobs inside so can actually use your best job for important content/parties

And level sync up will make you have your complete skill set if you so want to practice more the job you are leveling

You could argue that people could not touch their job at all and level it to cap but well you can also level all jobs just doing MSQ roulette and only half knowing a couple of attacks so people having to learn their jobs at cap level already exist.