Ace went to Onigashima after witnessing all the mistreatment that Kaido inflicted on the people and the country of Wano. He had no reason to hold back initially against the first opponent he encountered. The idea that Ace was holding back is nothing more than a HEADCANON on your part, honestly. What do you mean by that? If your intention is to belittle Yamato, then no. If your intention is to say that Ace could potentially be equal to Yamato using his Devil Fruit, I might even agree with that, man.
As long as you're willing to acknowledge that Yamato is also very strong, that's essentially the best path for you because there are far more arguments proving that Yamato > Ace than the opposite. Proposing a Yamato ~ Ace is beneficial for you.