From VG247: “Sekiro: Shadows Die Twice creator Hidetaki Miyazaki has admitted that those bosses youre finding so hard were in a completely different order during the games development.
Speaking at Reboot Develop today during an opening keynote with Shadow of the Colossus creator Fumito Ueda, Miyazaki said that he switches boss positions in his games a lot during game development.”
Source: N4G PC Sekiro bosses were in a totally different order until shortly before release