Job points, like the great Stompa already said, are by no means necessary. People make them necessary (BST, BLU, BLM, SCH gifts are all very good) but they aren't the end-all. In fact, with the exception of BLU, most jobs can compensate the lack of gifts with gear, granted with lower damage output and missing some spells but the job can still be very good in whatever event.
JP gets easier to get as you go along. Just do 10 a day or so and soon you'll see that you'll be getting 15 in that same amount of time. Soon it'll turn into 20 and 30 a day in the same amount of time. That's just solo in Escha or Reisenjima. In a party, you can clear 50-100+ JP in an hour depending on the party and how much JP you start with. Post 1200, you can easily get 200+ JP in an hour, going from 1200 to 2100 in one day.
Edit: Forgot to mention: having JP and gifts across jobs makes the whole system moot. The only gifts that you could argue could be cross-job are CP bonus and SU1 and 2 gifts, since those affect your character.