Adesanya, meanwhile, suffered the first defeat of his UFC career in March, a decision loss against UFC light heavyweight champ Jan Blachowicz.
He then rebounded to beat Vettori via a comprehensive five-round decision in June.
While the Kiwi earned every round from the judges, Whittaker said the performance was a long way short of how Adesanya had been hyped up.
"Watching that fight against Vettori, you can see he's not untouchable," Whittaker said.
"It reinforced the fact that he's very human. Very touchable.
"I actually thought his performance was average.
"Not average in the context of being bad. But he (Adesanya) never did anything more than what he had to do.
"He didn't do anything flashy. He didn't do anything more than necessary.
"Which is a good approach.
"But it certainly doesn't put you in the realm of the Gods."
So Israel Adesanya isn't a God?
"He's definitely not a God," Whittaker laughed.
"He's a very good fighter, sure. But he's not as good as he thinks he is."
Currently, Adesanya is undefeated in 10 UFC middleweight appearances and sits third in the organisation's pound for pound rankings, behind only Jon Jones and Kamaru Usman.
"And I understand why he's been blow up to seem untouchable, on a different level to everyone else," Whittaker continued.
"But I think his loss to Jan, followed by his average performance against Vettori, it just confirms that he isn't as untouchable as everyone thinks.
"Obviously, he's already beaten me once so deserves to start our next fight as favourite.
"But I'm a much different fighter now. A different person.
"And I know I have the tools to beat him.
"So I look forward to seeing what happens later this year."
Quizzed on the UFC 263 performance of Vettori, who lost a split decision to Adesanya back in 2018, Whittaker continued: "In a lot of interviews before the fight I mentioned that unless Vettori brought something different, it was going to be a repeat.
"And unfortunately for him, he didn't bring anything new.
"His approach in trying to get Adesanya down against the fence, it was a poor choice.
"And who knows? Maybe he didn't have any other option.
"Maybe it was too hard to get him down any other way.
"But for a tall guy like Adesanya, trying to take him down off the fence is a nightmare.
"In fact, the only time Vettori was successful there was when he really muscled it out, and you could see sapped a lot of energy from him.
"After the first and second rounds, I didn't need to watch anymore. You knew how the rest of that fight was going to go".