I wouldn't have picked O8S as an example of a 'challenging' uptime fight. Most of the modern simplifications to raid design have their origins in the Omega raid series, including self-positioning bosses. Players don't need to be able to achieve the 'theoretical maximum' uptime for a fight - if nobody can pull it off perfectly, you have a skill differential. They should just keep the boss targetable and see what players are capable of achieving.

It would be nice to see more of the 'reaction-driven' mechanics that Nakagawa was discussing. P12S had some interesting mechanics, but it felt like they deliberately slowed the second part down a bit too much.