Vegeta was badass in his first fight, it took basically EVERYONE important to beat him.
Then he became a loser. He made some moves on Namek but was still an ant compared to Frieza. He was a scrub compared to a woman android. He made Gohan get his arm hurt vs. Cell. He had to get steroids from Majin Buu to compete with Goku and did a suicide attack that didn't even work against Buu, then came back and "distracted" (read: got his **bleep** kicked) by Buu while Goku charged up.