Someone definitely mentioned this elsewhere already, but what probably happened is, by the time they started actually getting feedback about Endwalker... Things like the positive reception of PVP design, the frustration over the simplicity, etc. It was already too late for Dawntrail. The design was locked in, and for whatever reason, the development of FFXIV is 90% on rails and is not allowed to deviate from those tracks outside of what is otherwise deemed "drastic."
And that's really a shame. I think it's such a disappointment that jobs aren't allowed to receive more drastic adjustments during an expansion rather than only at the beginning of one. It's 2.5 years... And you're telling me there's no time at all to work on and develop a job identity rework at all between any of that time? Honestly, since the solo-players got to siphon development resources for the development of the duty support system throughout all of Endwalker, I'd appreciate the same amount of effort go into a job design reboot, even if it has to be staggered throughout all of Dawntrail.