DPS role subdivisions exist the way that they do for a few reasons. First, you only really need three varieties of DPS LB3 (single/line/AoE). Second, people tend to prefer playing at range, especially when starting out; this is as much for the psychological distance as it is because its mechanically safer. Lastly, if you are melee, you tend to become very possessive of space around the boss. You don't want more 'melee-types' to trip over.

We're fine when it comes to numbers for melee jobs for a few expansions at least. What I'll be interested to see is if they'll actually release both a caster and a ranged job at the same time next expansion (Time Mage/Chemist?), or if they'll opt for just doing a single job. With 19 standard combat jobs, I can't see it being feasible for their present job design team to continue adding jobs at the current rate.