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.