They deliberately went against this by design.. i cant rememebr the exact words they used but it goes back to ARR and them basically saying they wouldnt make other methods of levelling as fast or as viable because it would make it difficult for players to progress.. if grinding fates was just as fast or faster than dungeon queues for example then poor timmy who needs to clear the vault for the story is screwed because noones queuing dungeons or levelling roulettes.
There have been numerous ideas of fixes though. that would help those levelling dps jobs. from things like making roulettes reward EXP boosting scrolls instead of just a flat EXP boost. so i wanna level my lol drg. which i havent touched since 1.0. then i could just burn a roulette on my paladin get a scroll and use that scroll on my dragoon to gain a massive chunk of exp.. everyone wins.. i get a faster queue by queing as a tank but still able to level my dps. job. the dps gets a faster queue because theres more tanks.. and sure people might pipe up about how you wouldnt know how to play drg at 90.. if you levelled it with scrolls.. so what.. the levelling process teaches you nothing anyway especially if the roulettes continously put you in 50-60 content...
in my experience though its healers that are the problem currently. its not uncommon to open the duty finder and see green on the AIN all the way down the list..
the other issue and this they learnt from heavensward is that job balance really doesnt matter at all..
In ARR for example there was 2 tank jobs, 2 healer jobs, and 6 dps jobs.
in HW there were 3 tank job, 3 healer jobs, and 7 dps jobs. and the devs thought that by increasing the number of tank and healer jobs, more people would play tanks and healers.. that didnt happen
what happened was most of the people that picked up dark knight for example came from either paladins or warriors and as such were already laying tanks.. the same with most of the people who picked up astrologian.. they came from people who had played whm or sch..
in terms of role distribution the ratio of tank / healer players to dps players really didnt change at all. and on the whole it still hasnt even with 4 tanks and 4 healers.. and it wouldnt change much with 10 tank jobs or 10 healer jobs.