Some of this has already been said, but maybe collectively it'll help get some changes rolling:

State of healers. I actually just ran The Great Hunt normal earlier and that fight alone sums up healing in general: In 90% of content I'm barely doing anything. To the point where I wish I wasn't there or was an actual DPS. As an AST I have cards to deal with some boredom. I feel sorry for my co-healer WHM and SCH mains.

Can also include State of Tanks and some other DPS jobs in there. Tanks don't feel different other than effects. Some DPS, while not struggling, could use some major quality of life changes. I don't main those classes so I cannot comment on them. We all know who they are.

Lack of communication for western audiences. I get it. Square is based in Japan. That audience is the major focus. But when you have a 73 (and possibly still going) page asking who has quit healing, when you have several various different posts asking for DRK changes on the English forums, I think you should address that. To add onto this, and sorry if its going back to point 1, there was 0 communication about any healer questions, and for the most part that has remained. Why? People feel ignored and its pushing them away from the game.

Content design. Oh boy is this a doozy. Dungeons this expansion aren't hard at all. Maybe I'm old fashioned or maybe it was never this way, but I thought that dungeons were there to teach you how to use your kit in practice for Raids/Trials and Savage content. They do not. And they should. I shouldn't have to go into Savage level content to make the most out of my kit if I'm not a dps. I should be challenged to do so in dungeons so I'm prepared to do it even better by the time I get there. Tankbusters should be more frequent. Raid wide damage should be more frequent. If healers are forced to have so much healing in our kits (cause healers) make the content match.

Since its partly related, older fights while synced (CT raids I'm looking at you) need to be relooked at in the ilvl department. We shouldn't be able to skip phases as we are right now.
I could also extend this to somewhat dead content (like FATEs outside of Yokai event) but word limit.

The Devs do not feel that it is ok for X to be more difficult than Y. Aside from Savage/Extreme vs normal content. It is ok for certain jobs to require more skill than others. If a person wants to get better at a job, they will learn to get better. If they avoid a job because its too high skill for them, that is also fine. You do not have to, and should not, make jobs easier and accessible for all to play. People who want the higher skill will automatically be drawn to it. Not everything is for everyone and it shouldn't be.