You can always level your other classes when the content is somewhat dead, but I think priority right now is to cap your Eso, Void Arc(which is a somewhat good way to gear up) which gives a upgrade for your eso gear from i200-i210 and a Void arc gear at i200. Leveling can come much later.

Since your Ninja is at 60, you already have most of the mandatory skills, except B4B which is at 34 and that your dragoon is at 30. Anyways hope this helps.

I have played other games especially F2P Games where they literally hand things out to you as long as you pay, I am not biase but personally I think FF is great. You have developers that don't nerf/buff classes just to get players to change class and spend thousands of dollars on the new hype. So yeah try not to quit, but if it doesn't work for you no one can really stop you. Either way good luck.