This topic is my issue with the game as it currently stands.
I find no incentive whatsoever to level up another class to 50 and gear up that job. IMO I'd just be gearing a job in i70 gear to do AK and WP with.

My way of thinking is that if I were to get the "urge" to go to coil on another job I would not only be gimping myself, but the entire group. If a group wants to perform at their peak they need everyone at theirs. So while I70 crafted gear 5x meld is very good, it is still a step below the I90 gear. Me taking up a spot in my I70 gear with no intentions at all of "main-ing" it means that I will never invest myths into this job, meaning no +1 weapon or Myth armor. Where-as another person who's invested myths could take my spot and (assuming same skill levels) out perform me.

The only incentive I see to do CT is to gear sub jobs. Hopefully this helps.