Is there a reason in (DBZ anime only) Goku was always stronger than Vegeta after the Saiyan saga, outside of plot?

When they first meet, Vegeta is 3 times as strong as Goku. As Goku had to use 4x Kaioken to beat Vegeta’s beam and at 3x Kaioken their beams were even.
Once they get to Namek, Goku is stronger than Vegeta and basically every other soldier we see. Then as they explore Namek, Vegeta closed the gap a bit, but Goku fully surpassed everyone and stays far ahead of Vegeta.
That’s also a general event, Goku is weaker than many characters but eventually surpasses them in a short amount of time and then that character never catches back up to his power. This happened with every Z-fighter vs Goku. Gohan being the exception.
Obviously Goku has to be the strongest because he’s the main character.
Is there some cultural theme or overall theme of the show that causes Vegeta to always be 2nd best?