I feel like I'm a bit late to this topic, but here are my 2 cents.
I love how balanced FF14 is when it comes to everything.
The reason we have so many tanks and healers in this game is that they are not a pain in the a*s lvl'ng, unlike in games like wow, where it takes three times as long for a healer to kill anything than any DPS and tanks are almost as bad with the exception of the Death knight the only 2h weapon tank.
So before anyone asks for changes, ask your self do you want to wait in a dungeon queue for 30-60min because no one wishes to play a tank/healer because they are simply boring to lvl or do you want a good player with a healer who can out DPS a bad DPS player?