Cell is shown to be an intelligent enough character that he hid from Piccolo to get stronger and sweet-talked Vegeta after having fought them both. He had already fought Goku. When he was proven to be wrong while being arrogant, it was due to his ego blinding him to someone's much greater ki (SSJg2 Vegeta, etc.), the same way Gohan-Boo remained oblivious to Vegetto's superiority.
And yet after being outclassed, he openly acknowledged he needed to absorb him to win, and remained wary of Vegetto's halves until he learned they can't fuse anymore.
Much the same way, Zarbon remained arrogant to Vegeta until realizing their last battle gave him a zenkai, at which point he flipped out and realized he might be in over his head. If these other villain characters with similar arrogance had the sense to analyze their opponents' power like this, there's no cause for Cell to be wrong about Goku, especially when Goku was a great deal weaker than Cell's full power and hardly registers the same threat as SSJ2 Gohan. He also ceased to underestimate other opponents after fighting them once, while also realizing he couldn't presently defeat them. And if Cell openly recommends Goku to take a senzu to make the fight fun, he hardly is being pressured into a corner by the prospect of fighting Goku. Above all, Goku himself surrenders to Cell thinking only an enraged Gohan can defeat him.
You have no case, but I rest mine.