If Goku was a magnet for powerful evil, then he should have stayed and confronted that evil, instead of placing the burden of responsibility on his son, who isn't a fighter. Goku chose to protect the Earth. Gohan had the job chosen for him.
They did worse than die. They made the villain even stronger. They were terrible fighters; if they had an ounce of common sense, they would have destroyed Buu. Instead they decide to make the fight "dramatic" by holding back until 30 seconds before the fusion ends. Power means nothing if you are too stupid to use it. Goku knew nothing about these kids; he shouldn't have put the fate of the universe on their shoulders. Especially when he knows that he could do it himself.
Kaio's never shown any limits on his telepathy before. I don't know there you're getting the minutes thing from.
Goku says himself that he could have beaten Buu. There's no reason to doubt him.
Gohan was far stronger than he was, and he thought the evil was going after him. If they went after him, at least it would be in the afterlife. And even if Gohan wasn't a fighter by nature, there's little reason why he couldn't have trained and studied. He didn't, he slacked off. Gohan may not have been a fighter, but he accepted the mantle. At some point, the training wheels had to come off, Goku can't always be there to save the day.
They weren't terrible fighters, just cocky, there's a difference. Gotenks is for all intents and purposes a different being, and neither Trunks nor Goten were cocky, green, sure.
Your point about Kaio is pure conjecture. I got the minutes thing from the fact that Kaio doesn't typically talk or let people talk for that long and he only lets If it's as you say it is, then that creates a plot hole because then there would've been little fear of having enough time to teach the dance, he could've just taught from the other world.
Goku also told Piccolo he couldn't beat Buu. The best explanation Toriyama could give was that he lied, but why would Goku have lied about that?
Gohan completely outclassed Cell. The only thing holding him back was his emotions. With a little training, he could've fixed that problem. He didn't have to be enraged to defeat Cell, he needed to be enraged to turn SS2, which after that point was completely under his control. Also, his sudden desire to not want to fight came completely out of nowhere. It was a Toriyama trying to create drama.
The biggest truths aren't original. The truth is ketchup. It's Jim Belushi. Its job isn't to blow our minds. It's to be within reach.
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