How is being passive good for drama?
Drama can come out of literary anything, that's writing 101. In this case, it's because it clashes with Goku's personality.
Telling Cell "this is pointless" doesn't flow from Gohan not believing his father and being defferential to him. Confused? Sure, but this something ele entirely. It also doesn't flow from Goku giving up that Gohan would give up or need his hand held. I know Gohan was ready to help at the beginning of the arc, and that should've been him throughout the arc.
Actually it flows so perfectly, I'm a little surprised you brought it up. The reason Gohan tells Cell the fight is pointless is because Gohan is certain of his victory
and that is because of Goku. Because of how much he believes in his father and his plan. He understood that his father's idea was to have Cell get him get angry and then defeat Cell with his rage boost. He is not trying to weasel out of a fight, he is trying to warn Cell because he doesn't want to kill him.
And that is him throughout the arc, that is his disposition at all times.
I know what is a narrative issue and what's a character issue. He's eager to help when he's in the background, but when it's time for him to step up, it's all Gohan needing his hand held. The explanation I often get from fans such as yourself is he changed in the Room of Spirit and Time.
As in it's not Gohan's growth getting reversed, or him being written out of character. He is the same as he was in the Namek arc, just as brave, just as eager, just as responsible- he just isn't used as much for a good portion of it because the story focuses on other characters more. I feel like I've written this a thousand times already. The only time he needed his hand to be held was when he lost his will to fight at the end, otherwise he simply being his usual deferential self.
Him being different after his time in the ROSAT isn't something I considered. He seems a little more mature and serious, that's true, but that just might be incidental.
So I think it all boils down to confidence.
It is a confidence issue as well, but self-confidence. Confidence in his father is another thing, and that he has in spades. As I said. he understood what his father intended when he chose him, and technically he was right about Gohan's anger being the key. It backfired at first simply because of the unforeseen emotional turmoil that neither had predicted would occur in Gohan.