At least for WoE, the reason why expanded jobs don't get any attention is because of that low 12 members cap per guild. To point out: back when cap was 24, we had some Kagerous, SR and SE being used in WoE.
fey
Expanded jobs, for WoE, goes to the same place as RK: why should I run it when I have a class that does the same thing but better?
I'm no Kagerou player, but, a job that has full FCT reduction, physical damage immunity, self pneuma and many other tools don't look that underwhelming to me, honestly. But is undeniable that we have classes that are doing it job better in current meta.