Don't know if this adds nothing right now, but I guess I got this in my head and wanted to thow it out there, and this feels like the right thread to do so.
I think, even more than the fights themselves feeling more or less underwhelming (I think Robin's is great, Franky's is fun but too short, Jinbe's has good coreography but is too easy and marred by bizarre exposition dumps and Nami & Usopp's is the worst One Piece "fight" so far), the most disapointing thing for me about the Tobbi Roppo is the fact that they had so little time to show themselves.
Say what you will about the Dofla family. It's true when push came to shove, almost all of them ended up being disappointing, but the thing is, we had them shown onscreen from as far back as Punk Hazard. We got time to see their personality quirks, we got to see their "roles" throughout the arc. Some of them ganged up on Franky, Giolla attacked the Sunny, Diamante was the Colosseum guy, Dellinger was sent to "kill" Bellamy, Trebol guarded Sugar, etc…We had them do "stuff" before the final fights. Hell, they had a flashback as a "family". It's weird the Flying 6 weren't allowed that, when they are actually a pretty interesting bunch that I feel worked well with what they got (Ulti is now a favorite, for example) but were introduced on chapter...978? Of an arc that started on chapter 909?
Honestly, I feel this IS a wasted opportunity. Little things would've worked perfectly fine. Like he did with Page One, Oda should've 100% springled the Flying 6 throughout the Wano arc. Have Sasaki show up to drink sake with Kyoshiro, so we know they have "history" as pals. Have Ulti bandage Page One after his fight with Sanji, while Page One complaints that "it doesn't hurt, leave me alone". Have Black Maria test the Oirans that'll go to Onigashima during the fire festival (a shamisen playing test or something like that, where she kills one that messes up a note or something). I know that then messes up the "introducing the Tobbi Roppo!" chapter, which was a cool intro and everything, and I really liked those chapters where the Tobbi Roppo got to bounce off one another and interact with the Calamities and Kaido and all that. It is good stuff! But maybe we could've seen them beforehand during the arc. . .WITHOUT us knowing they were part of the Flying 6, so when they are revealed we go "oh, that giant lady was one of the flying 6! as was Kyoshiro's drinking pal! so they are big shots indeed, huh!".
And that's it, that's the thought I had.