Longer term planning and strategy happens, just not in lower level content. If you look at say the second half of O12S with Final Omega, one spot I seem to recall being difficult to figure out how to cover for the healers (I must admit I don't heal in savage so this is mostly from the discord discussions during raid) when we were learning it is the Ion Efflux after Patch, then having to go into Hello World and figuring out how to best utilize cooldowns and get coverage for all the people who have Critical Synchronization Bug, deal with the Critical Overflow Bugs and have everyone healthy enough to survive the second Ion Efflux.
The same thing could be said of quite a few of the savage encounters - the problem is the bar outside of savage raiding is so low that you don't have any real decisions or planning to make.
And that doesn't just apply to healers. In an Ex Roulette, as long as the tank and healer are doing sufficient DPS, the actual DPS can basically play however they want and all it will do is slow down the chain pulling. I imagine that even if the tank and healer are strictly sticking to only heals and only aggro combos in tank stance the DPS could STILL do basically nothing and while the instance might be abysmally long would still likely be doable. Who would actually put up with that is an entirely separate matter.
Tanks, similarly, don't require a whole lot in dungeon/24 man instances. Keeping aggro is about it - and you don't even need your actual aggro combo to do that anymore. Maybe because I play one the vast majority of the time I might nit pick here, but most of what I want to see is QoL stuff like not stopping to mess around with mobs when you are pulling multiple groups and making sure to cycle through cooldowns properly on bigger pulls. That last one might be more required if you do bigger pulls, but pulls like that aren't necessary.
That being said...
My wish for the expansion would be to massively prune down skills. No one should need 3+ hotbars of routinely used abilities. A standard rotation minus cooldowns and stances shouldn't take up 2 hotbars. In most games a convoluted way to control your character is bad game design. I don't know why that shouldn't hold true in an MMORPG. I'm not asking for a jobs to become more mindless. They can give us procs to watch or a priority system or something else so we aren't just mashing the 1 key or the X button and can still make intelligent decisions.
You could still have complicated design without forcing people to remember the often-times John Madden style openers. With raising the floor on character ability, maybe they could do the same to regular group content. Maybe an Ex Dungeon could be somewhere in between where it is now and an Ex Trial.