Rather than going specific to any job (as we have dedicated forums for that), I'm going to approach this from a different angle and tackle UI that every job would benefit from seeing.

Party lists showing the last action a player used, even if it was an instant-cast spell, weaponskill, or ability. This would all exist in the same space as the castbars do on the party list, with their GCD and auto-attack timers potentially being included as an option as well.

Heals having some sort of class-specific indicator that indicates who they are targeting, or their placement if AoE. Ideally hardcast heals would sustain this, but instant effects could briefly flash their indicator as well.

The reason I want this is not because I'm unfamiliar with AoE ranges or cast-times on heals or unable to figure out what another player is doing, It's because the average roulette player doesn't know how to figure this out and I'd like to be able to point out obvious flubs in a rotation or lack of (or proper carrying) effort on someone's part without resorting to the thing we aren't mentioning. It would be nice to say "Hey you screwed up X during Mechanic Y, did you need help?" and be able to point to an in-game reference to explain how I noticed without having to explain the aggro list every time.