Though, the difficult encounters are made difficult through the complexity of additional mechanics across the board.
They don't need to filter those down through game modes at all.
All the suggestions I've made, are to the base behaviour of bosses. Which are completely separate to the plethora of "Don't stand in the bad" mechanics that define the actual difficulty of XIV's encounters.
It's not putting more responsibilities on them, it's shifting their responsibilities.
Shifting from being focused on pumping out maximum DPS, to instead focusing on their actual role (Mitigating/Healing). It doesn't make them any more or less important. In Savage+ content, people are already pushed to maximize DPS to beat tight enrage timers (Of course, these enrage timers would need to be addressed after such changes). In normals, Tanks and Healers are vital to keep enough people standing to have the fight continue (Since, given the lack of enrages, that's all you need to beat encounters, hence why LB's are typically reserved for Healers to mass raise everyone when people inevitably mess up mechanics and get one-shot en masse)
Considering the current state of the game, where Healers are severely lacking in number these days, BECAUSE they had their responsibilities and engagement ripped out thanks to dumbing down of filler DPS duties with no change in healing responsibilities. I doubt that is the case.
We even have a thread over in the Healer section that is getting more and more full of long term healers who've quit healing to go play DPS jobs because they offer more engagement.
So... Why is it that we need to let braindead healers and tanks continue to function? We don't let braindead DPS get away with doing nothing, with various DPS checks (E8 and Cinder Drift both have phases where the boss just spams AoE until death. E7 has the adds that need to be killed before they explode and wipe the party. Even way back in ARR content we had things like Ifrit that required killing of the nail before he nuked everyone)
If people perform poorly, they either need to learn, or get kicked.
If a Tank dies, the OT will get hit.
Unless you mean Dungeons where there is only 1 tank. In which case, well, currently, tanks are not necessary since you can just heal DPS who have aggro from their high damage given the plethora of healing tools available to healers... (Thus, if simply using those tools on the Tank then the Tank shouldn't die. Especially if Tanks have more things to do to keep themselves alive other than "Sit there being inherently tanky from defence")
It's not going to inject frustration into the game to make people actually have to play it.
As it stands right now, passive damage taken by tanks is pretty much covered by applying a Regen and Shield to them. Meaning that for the other GCD's between "Busters", healers spam nukes.
Simply increasing damage frequency to replace some of that nuke spam with GCD heals, shouldn't make things more frustrating, unless someone is only playing healer so they can spam nukes all day (Though, from what I gather from healer reactions, that's the exact opposite of what they want to do)
Though, that's what this sort of change is supposed to address. Going forward with encounter designs that specifically include more damage, allows for the class design team to focus on creating more parity in classes ability to function in the role. As opposed to now where their entire balance decision revolves around making sure all the jobs do equal DPS.
More emphasis on mitigation and healing means more focus on balancing mitigation and healing. More making Tanks actual tanks, not Blue DPS and more making healers actual healers not Green DPS.
Shifting the healing power towards GCD's doesn't mean deleting oGCD's. It just means that instead of oGCD's being like 1200 potency and nigh full healing a Tank in one go, it will be less potent like ~400 ish potency heal to use as a bonus to throughput.
If anything, shifting the healing power towards GCD's and reducing the overall potency of oGCD's can result in MORE weaving potential, as CD timers for oGCD's can be reduced since they aren't in danger of completely trivializing all damage dealt in an encounter by simply healing through every attack for 0 MP and 0 GCD cost.