They kinda did.
Nami didn't die due to sheer "Oda" power. One headbutt from Ulti that she took should have shattered her skull completely and killed her on the spot. Same for Usopp.
Jinbei only managed to "outclass" Whoswho on the chapter of their fight. But they were fighting for quite a while and Whoswho actually managed to pierce through Jinbei's Haki, but, again, "Oda" strikes again and suddenly Jinbei gets more powerful due to being pissed at Whoswho racism.
Franky been fighting Sasaki for a long time as well, and that using his Franky Shogun. He almost got clapped in the end if it wasn't for the eject button, so he could shoot a final laser at Sasaki. But if the laser had failed, he wouldn't have the Shogun anymore, and that would be a problem for him, since he probably wasted almost all his cola fuel.
Here with Robin seems to be quite the case of the enemy severely underestimating Robin. Not that Maria didn't have a chance, but she thought she could "torture" and "toy" with Robin for a while, instead of just going for the KO, but Robin showed great physical prowess and held on to launch a counter attack, finishing Black Maria with an amazing hellish demon clone.
Problem with all these fights is just that they are basically 1 chapter long. Last chapter was just Robin and Brook running from BM and dealing with the SMILE on her weapon, but the fight itself just was this week's. And, for Jinbei and Franky, a good chunk of their fights were basically offscreened, so Oda could grace us with that amazing Tama plot that we ALL wished for.
And a gifter coming out of a chicken's ass.
My only problem with the Flying 6, is just that, instead of showcasing them, Oda wasted A LOT of time, not only in Onigashima, but Wano in general, with a bunch of gifters that he just felt like drawing. Couldn't he do some special SBS like he did Roger's crew to showcase these fucking atrocious gifters? And give more panel time to the enemies that actually matter.
Flying 6 are literally just some enemies that appeared for the final battle. They could have been way more memorable, but oh well. At least I had fun with these fights, despite the rest of the arc being complete garbage.
But I fear the times when the best thing about an One Piece arc are just the fights, while the story aspect is just bad.