"Let's recap Sanji's backstory even though it'll be recapped in the upcoming special anyways!"
Different audiences. People who watch the special may or may not faithfully watch the anime, and vice versa. They do this so both audiences are informed/reminded of Sanji's back story that was aired (in full, not just pieces) on TV over 15 years or something ago. People always complain when we get recaps of earlier material yet no one seems to understand that this is a business that is very different from the manga industry. The TV industry has to constantly focus on getting new kids into the show who aren't familiar with material that happened years and years ago. The difference between Oda in the manga and the anime airing on TV is simple and straight forward:
-Casuals reading Jump who stumble upon this particular chapter would be like, "This Zeff guy seems cool. He and Sanji seem to have a history. Hmm, One Piece manga volumes are on sale at the local book store for like 8-9 bucks (convert to Yen) and that volume shows the back story of Sanji and how he joined Luffy.
- Casuals flipping through channels on TV will surely have heard of One Piece given its popularity in Japan but may not be that familiar with it, especially kids just checking new shows out. Some kid happens to come across this episode and say the recapped flashback wasn't shown, they would have literally no clue who Zeff is and finding the DVDs with only 3 episodes a pop for around 50 bucks (again convert to yen) or higher due to being low stock or not even in stock anymore (or the super expensive log sets) or maybe for rent at some old rental store (if you're lucky). Showing the flashback ensures new fans are onboard and can follow the current plotline, There's also the fact that I feel a kid reading a Jump volume would be less likely to close the book due to lack of understanding something compared to a kid holding a remote who may just flip the channel to Japanese Spongebob or something.
There are times when the flashbacks are excessive, unnecessary, or understandable but badly placed (that one episode before the Zou arc or the Enies Lobby disaster) and there are occasions where the flashbacks are fitting and timed perfectly such as this one, the Laboon case with Brook (lacking new animation back then) or the Nami flashback during Fishman Island.
So Toei bring out Luffys entire move set, the king gong gun which is an island splitter against cracker.
This is a joke. The filler has gone too far
Why is this such a big deal to you? It is clearly stated in the manga that
! Luffy had to go Gear Fourth against Cracker numerous times which more or less not just heavily implies but confirms that Cracker's defenses could tank anything Luffy dished out until the new move he pulls after the 11 hour fight. Him using a move that destroyed the entire island of Dressrosa to take out like 20 biscuit soldiers that could block a single Kong Punch is not really that outrageous at all. Granted they didn't show how Cracker himself could take the hit of King Kong Punch directly (after all Cracker in my opinion is at least the same level as Doflamingo or just under it, but not stronger than him).