Everyone uses a priority if they use a rotation. It's just that when the same priority repeats over and over it's called a rotation. Also, I do use a priority system... diseases > OB > BS/Pest > FS > HB > HoW
However, there are circumstances where I will completely skip a rime proc due to always being able to use something else. Another is when I have 3 seconds until next OB with 32 rp, using HoW then FS to maybe get a KM proc rather than FS -> KM -> HoW. Circumstances such as these defy the "set rotation" because I choose to put priority in other places.