The Straw Hats seem to grow at an exponential rate in this one arc. Even more so than they did all of pre timeskip combined.
He literally struggled like hell against Big Mom’s Commanders. Needed help in both fights, and most likely would have lost without the plot convenience.
Now, an arc later, he has gained the Future Sight ability+ Advanced Conqueror’s and Armament Haki, damaging Kaido in base as well as exchanging blows.
Honestly we’ve seen Luffy display his abilities in 1v1 fights against strong characters. Although it was incredibly fast he learned and trained to gain the abilities he has.
He has defeated multiple low tier opponents but he never had a fight against a Commander tier opponent.
Now Zoro can use Conqueror’s Haki, a very rare form of Haki whose users are stated to have the qualities of a king. He strengthened his “Kyutoryu: Asura” using Busoshoku and Conqueror’s Haki, which allowed him to leave a permanent scar on Kaido in his hybrid-dragon form!
Previously he somewhat struggled against characters in a similar tier to what we now call Tobiroppo. He wasn’t below them but it didn’t seem he could defeat them easily in a straightup 1v1 fight. And he lost pretty easily to a character on a relative tier to Kaido’s Commanders. Sanji never even got to have an actual 1v1 fight to display his abilities. He essentially went from a bunch of inconclusive clashes with mid/ high tier characters.
Now he’s currently fighting a Yonko Commander 1v1 without the use of his raid suit.
While it is very cool, it’s crazy when you think about Luffy in Whole Cake Island.
She was previously too incompetent to handle raging army characters.
But now she has the power to stand up against and defeat a Tobiroppo member who is much stronger than the raging army characters.
Big Mom had to intervene but still…..Even after Big Mom’s interference Oda made Nami stronger by giving her an upgraded Zeus.