SRP76

I don't think Piccolo got as strong as Stage Two Cell. That form of Cell was about 4x stronger than Piccolo before he did his training, and Vegeta and Trunks only got 3x stronger (if that, even) when they did the training alone (which is what Piccolo had to do; he had no sparring partner).

So, if Piccolo got 3x stronger, he wouldn't surpass someone who is 4x stronger than he was.

I feel that Piccolo's pretty useless by this point in the story.