Protagonist builds depend on your Protagonists class. You can change if you want, these are only reccomendations. Protagonist should have the following depending on their class:
Swordsmen: Physical. They should be Tanks although they can have some damage output as well.
Sniper: Physical. They should be fast and do a lot of damage.
Navigators: Magical. They should mainly have a lot of damage output.
Doctors: Magical. They should be Tanks with healing and team support.
Feel free to stray away from these as you might want to go on your own path. At around level 70+, Tanks arn't needed too much so you can change your build then if you want to change.