Future Warrior said:
Ok, fair enough.
Vegeta during the Namek arc was cautious and patient because he's greatly aware of how dangerous Freeza and his army could be. He's willing to take precautions in order to gain the best chances of getting his wish for immortality. He has no reason to kid himself that he can steamroll his way with no fear when he's been his underling for pretty much his entire life. But we can still see a glimpse of his cocky and arrogant attitude when he believes himself to be far stronger than Freeza, until he gets quickly dominated with ease.
Witnessing SSJ Trunks and Goku showing off power far greater than his own despite the latter being a lower-class warrior was an even greater insult to himself. You could argue all you want that he doesn't care whether or not Goku is stronger than him or not, but the Saiyan arc clearly demonstrates how he feels on the matter. Just to prove my point, I'll include anime filler https://www.youtube.com/watch?v=1O5wnzrXUlY. By the time the artificial humans have arrived, he's become a SSJ and believes himself to be the strongest warrior in the universe. Even Piccolo thinks he's surpassed Goku. From that point on, he's constantly trying to prove himself that no one is better than him just to sate his own ego. His decisions are ''dumb'' but they are all due to his narcissistic nature. If he wasn't a SSJ at any point in the arc I honestly don't think he would make any of the reckless decisions he made.
DB isn't complex but the characters are very true to human nature, more so than many other anime I've seen.
While it's true that Vegeta took those precautions because he knew how dangerous Freeza was, we also caught a glimpse of his pragmatic nature back in Saiyan arc. When he sensed that Goku was at 5,000, he ordered Nappa to kill Piccolo and the others to keep them from being able to help him, as well as shaking him up. Also, he and Nappa picked a Full Moon Day in case they would end up having trouble (which they did).
Plus, Cell Arc Vegeta already knew how dangerous the Androids were, especially when Trunks explicitely told him so. He should have known that getting Super Saiyan wouldn't guarantee that he'd win. Now, he did get cocky, but never to the point of actively helping his opponent get stronger out of suicidal overconfidence.
As for "Taking Goku's strength as an insult" point, while true, again, Vegeta didn't actually make it an obsession until Cell Arc. Being the strongest in the universe sure is a consistent goal he has, but the consistent jealousy he had over Goku was established in this arc.