But for real: The biggest disappointment of them all has to be Toki.
I still kept waiting for more to happen, but that was it, Oda?
THAT WAS IT FFS?
You introduce a character from the void century with that much hype in advance and then you only let her mention her void century ties once (!) while also writing her the same boring way you write 99% of your female characters?
That's some bullshit not even the hardest homers can defend.
She served ZERO purpose. This entire travelling through time nonsense didn't serve any purpose either. Wano could've happened exactly like it did without Toki or any kind of timeskip.
Momo is a bit older (13 or 14 for end of arc purposes), Kaido invaded the country a few months ago (or maybe a year), installed Orochi, Scabbards faked their death and went hiding, while Momo, Kinemon etc. escaped on boat just like they did.
Et voila - literally nothing important changes for the story. Toki was completely redundant from the get-go.
Why would Oda reveal the void century further before it is time for it to be revealed?
How would that tie into Wano/defeating Kaidou in any way?
You can argue the time skip didn't help the war effort (if you assume they can freely manage to
somehow escape despite being the most wanted people in the island), you can't argue that it wasn't important for the story.
Momo wouldn't be a child, struggling with the burdens upon his small shoulders. He'd be a 30 year old with the strength of Oden and both of his swords, or at worst he'd be some cucked out Yamato level strength figure that desperately wanted to avenge his father but was just too weak due to his poor training over 20 years of revenge training.
He'd be a guy 15 years older than Luffy crying and asking him for help (which would invalidate the poiniancy of Luffy forcing Momo to be more than a figurehead).
He wouldn't have any tie in with PH, he wouldn't have the artificial dragon fruit that he doesn't know how to use struggling to save Wano.
He wouldn't have the selfless sacrifice of 20 years of lifespan to save his country
He wouldn't have the raw emotion, and fear of seeing his parents and country get destroyed in what was to him a mere few months prior to overcome.
Kinemon would go from a mix of a caring substitute father figure and harshly expectant retainer to an aged out scabbard who looked after Momo for years when he was young.