Cell believes that and is shown to be wrong. Gohan's Chi didn't go down one bit after Cell's attack. One thing that needs to be said is Gohan is doing everything he can to avoid fighting. That's the only reason why he appeared to be nothing special.
That's because Goku's best was unimpressive to Gohan. When Goku went full-power and blew everyone away, Gohan thought everyone was odd for being excited. Gohan is able to see that Goku's effort was really unimpressive. Vegeta thinks this revelation is not only impossible, but also a lie. What this shows is Gohan is the only one capable of seeing Goku's true power for what is..unlike the others.
It's simple. Gohan needed Super Saiyan 2 to defeat Cell. This requirement isn't necessary for Goku because Gohan's already stronger than him. To beat Cell, they need Gohan's dormant power.
That wasn't stated. Cell had the upper-hand. Even Roshi pointed this out despite only watching the battle on tv:
Bulma: “Wha—aat, that was so close! He was just a step away!”
Kame-sennin: “…No he wasn’t…It’s true that it looks like they’re having a good match, but…unlike Goku, Cell still has room for composure left…[ ] ...Goku can’t win…What’s more, to me it looks as if he knows that but is still fighting…I don’t know what he’s thinking…”
Goku was inferior to Cell in power and speed. In h2h situations, Goku always came out looking worse.
Gohan was only using his speed at that point. He didn't even try to attack Cell. This is why the speed is commented on. Gohan made Cell up his speed because he's stronger and faster than the last opponent that couldn't make Cell change his speed.
The word "surpassed" is used to denote superiority. This has happened throughout the entire manga. Why would AT write a title about Goku being surpassed right before he displays Super Saiyan Gohan's power? Because the story is plainly saying the warrior (Gohan) is superior to Goku.