There's practice and there's the final result.

Practice is just doing the rotation right and handling (Blm specific) procs to maximize uptime. how you treat procs and polyglots depends on the encounter. You might need them to move, you might get to dump them all in buff windows.

Final result is based on RNG. Did your potency dumps in the buff window crit? Did they roll high? (All skills roll between 95 and 105% of their potential damage).

This is especially true in critical hit set ups. Sometimes you crit. Sometimes you don't. Sometimes you crit on high rolls, sometimes you crit on low rolls. DPS can swing very high but it can also swing very low.