In Dragon Ball, when the character first makes an appearance, Vegeta emerges as a formidable antagonist, completely dominating the warriors from Planet Earth. From the very beginning, there has always been a rivalry between Vegeta and Goku, either directly or indirectly.
Moreover, the competitive relationship between these two characters is incredibly famous in the anime world and has captivated many fans. This ongoing rivalry has significantly contributed to their development, making them stronger and more refined over time.

The truth is that when Vegeta sees Goku as his rival, his main motivation becomes “to defeat and surpass Kakarot.” There are moments when the Saiyan prince becomes stronger and shines brighter than Goku.
For instance, there was a time when Vegeta confronted Beerus. When Bulma slapped Beerus for ruining her party, this action provoked the God of Destruction, leading Vegeta to unleash his fury. In Super Saiyan 2 form, he unleashed a flurry of powerful attacks and managed to land a hit on Beerus—a feat that Goku in Super Saiyan 3 could not achieve.
However, it is rare for Vegeta to surpass Goku. So, what is the reason behind this?
Akira Toriyama has hinted a bit about the Saiyan race and their inherent nature as warriors during his interviews with Weekly Shonen Jump. When asked whether Saiyans train to fight or not, Toriyama mentioned that the essence of a Saiyan is their love for battle. They are constantly seeking challenges across the universe, yet strong warriors like Vegeta often endure a rigorous training process that few can match.

Without a mentor, Vegeta has to learn everything by himself. He has reached a new level through his training alone. Whenever Vegeta discovers something new, Goku has already turned it into his own strength. There’s a saying that having a teacher is the best way to become stronger, yet Vegeta has had no one to guide him until Whis decided to train him.
In contrast, regarding Goku, Toriyama noted that “Some kids can fly even without being taught. In Goku’s case, he grew up on Planet Earth, where no one knew how to fly, so he spent a long time learning to fly.” However, once characters who could fly began to appear, Goku quickly adapted and learned how to fly.

Thus, the lack of a guiding mentor is a significant reason why Vegeta tends to be less powerful than Goku, but this could change as Whis continues to train Vegeta following the Tournament of Power.