I started back about half a year before Stormblood was going to hit. So I recall the need to level other classes for certain abilities and to unlock the more advanced jobs. While on one hand I get where this fell short, such as necessity actions like the gladiator's provoke or healer's cleric stance. But at the same time, I liked that things I did on other jobs made my 'main' stronger. That my character was taking knowledge from other jobs and becoming more powerful as a whole.
But now I feel like role actions and such we lost that feeling. I don't feel like I am really earning anything extra if my white mage is my main and I go spend time leveling my black mage. I have leveled a few jobs since Stormblood and honestly I feel like while it is easier to jump in and level jobs compared to before that feeling that your character is benefiting from spending time in other jobs has since been lost.
I strongly feel that the main draw from the job system in previous final fantasy games has been that your character is shaped by the jobs and time invested in said jobs to make the overall character more powerful. Such as in tactics where a caster spent time as a squire to learn how to use shields, or a knight having had archer experience can charge for a stronger attack. While I know we can't have anything quite so free form in this game, the point is that now our avatars feel more like paper-dolls with abilities and less like characters built from the time players spent investing in various jobs.
One simple idea I've had is having 'traits' you unlock at level 50, 60, and 70 that you can equip for small bonuses. Such as a trait from a scholar that makes the cooldown of shield spells/abilities slightly shorter. Or having critical hits with an astrologian trait give a minor random version of one of their cards. Just minor effects that you can unlock and take activate a certain amount of as you play various jobs; that overall can let you fine tune your character and reward you for investing in various said jobs.
But it doesn't have to be that. However I again strongly feel that we should have some form of interaction between various jobs correlating to our experience spent in them. That without it, it all just feels much flatter then what we had before.