Best way to learn is by doing.
With a new fighting game, I put into training mode, put the CPU at the max difficulty, and get thrashed between reading wikis and watching videos about the game.
I had a similar experience with XIV. I hadn't healed much in MMOs when ARR launched, so I had a lot of learning to do, and at 50, everyone wanted to speedrun AK. So I learned it, and now can confidently do any sort of speedrun in the game, and can confidently do speed runs of new dungeons after doing them once normally.
The community will not baby through dungeons like you and very few others seem to want it to. When there is a new person, groups will throttle themselves a bit if it's a new healer or tank, so that's already a non-issue.