No?
Because you run with 7 other people that can't push more then 1 button doesn't mean that it's hard.
The OP have some disabilities, cleared content anyway, but complaining still ? Because he "feels" carried?
8-man duties are 8 man, not single player. A group of 8 can clear any non-savage content just because they were able to get in. The fact one player can be at disadvantage because his own problems (any, not only disabilities but any) is already balanced by a difficulty level that makes the duty clearable even when the effort of one or two members is low. I think there is nothing to fix.
If OP wants no troubles on clearing content, just go overgeared and that's all. i345 now raining to everyone and you can do everything (excluding latest savage ofc) with it.
If you want feel better, Castrum Fluminis was hell to me too, myfirstsecond time (edit: my first was a party disband after half hour of wipes…) there was a number of wipes and then we cleared with only a mere 6s from the autokick. Yes we were there the full hour before the clear. This is the latest content of the game and it is natural you have (somewhat) hard time on doing it.
I think a complain because you cannot cheese it out at first try was an overreaction.
It's stupid. No one makes videos of barely struggling to play the game because of their disability, nor do you see the tons of people who can't devote every waking hour to a game in order to overcome a handicap through sheer repetition. There's this weird bias to the photogenic overcomers when talking about disabilities, as if every person in a wheelchair can learn to play basketball if they just put their mind to it.
Or they want the concluding boss to a large story arc to not be an absolute joke like Thordan normal mode where you could literally fail half his mechanics and clear without a hitch? It couldn't possibly that.
You're misinterpreting the intent. People aren't necessarily saying "because this person overcame x, you should be able to in the same way." They're saying, "this person didn't complain or blame the game because they had a disability. They found a solution that worked for themselves."
which probably involved spending an insane amount of time and effort, and that many people can or will not be able to do. The real "solution" ends up being not doing it or being carried through it, which is not much of a solution at all. But the video always makes the "git gud" people feel good.
That particular fight though is pretty unique in the speed of the mechanics in the last phase, and there should be a bit of discussion on how fast mechanics should be in casual content. I mean, susano ex fires off slower, and requires you to keep track of less elements for each mechanic.
Don't all final fantasy games get harder as the game progresses through? Why should this one be different.
Also, we really need to decide what casual means. Does it mean time put into the game or player skill?
The game is not too hard. This is a silly train of thought. If someone has to try harder at something because of an irl circumstance beyond the development team's control that is between that person and the game, it shouldn't involve anyone else.
The idea that they need to scale back the already 100% carryable story mode trials because of the needs of an exceedingly small number of players (thus hamstringing the enjoyment of a much larger number of players) just doesn't make any sense... particularly from a business standpoint.