So, the big fix to encounter design comes from recognizing 3 things.

1, healers are overpowered as all hell (at healing.)

2, tanks are overpowered as all hell (at tanking, specifically mitigations.)

3, binary pass-fails aren't fun. They're attention checks and they get extremely tedious, especially when it's the only way your role does its job.

In order to fix the encounter design, the devs need to claw back power from all healers and tanks. Even from casters, who have way too much movement right now for good caster design. You just can't make interesting heal checks when a healer can solve charybdis into second aoe for free. You can't make interesting tank mechanics when a paladin just using personal mit can hit 450% EHP. Hell, you can't make any tank other than a mitigation tank if you let mitigation values hit 450% EHP. You can't even do fun things like force healers to make actual decisions when spells like medica 1 exist.

Like, seriously, how do you threaten classes this overpowered? Almost every single design problem of FFXIV, including modern day DDR fights, is a direct consequence of healers and tanks being completely overpowered.

Fixing it can be done somewhat simply with a trait at level, say, 102, and a complete healer and tank swap (and adding cast bars back to casters,) could even be done without messing up older fight design. But the simple fact is all the problems of FFXIV game design stems from making classes too overpowered, and instead of depowering them, they double down and push the design ever more into the extreme. More one shots, more auto-deaths, faster mechanics, faster massive aoes. That's not interesting design, it just eventually hits a breakpoint and people stop playing the game.