and why did the heroes if they thought any single one of them could beat him, actually go along with it?
They couldn't beat him collectively either. And group combat can just make it harder to attack at times, unless you're limiting it to 1-2 people attacking at with guys rotating in and out to give fighters a chance to recover while slowly wearing down the enemy.... granted, Cell doesn't really fatigue the way a normal fighter would so even that tactic might not help.
Its been a long time but I recall him believing Gohan could pull it off.
still my point being though, why would you ever play by the villains rules. you never play someone at their own game and reasonably expect to win. but then again Goku was never shown to be a brilliant man, so I suppose I can let it slide on that alone.
Everyone thought goku could do it and they decided to take the extra time and train. ---