is one piece episode 851 filler?

Luffy confronts Katakuri in the Mirro-World, and although the Sweet Commander states that Luffy's recklessness has made him very dangerous to the Big Mom Pirates, Luffy is no match for him in combat. Katakuri's subordinates affirm this, stating that his bounty is greater than 1,000,000,000 and he is the strongest of the Three Sweet Commanders.

Luffy then attacks Katakuri, but Katakuri easily dodges all the attacks and hits Luffy with his advanced Observation Haki.