They are both Saiyans, they both train incredibly hard. However there are a few things Goku has that Vegeta never will (unless he wishes for them).
First is that Vegeta is older than Goku. I know it’s noy much, but it is a factor. You can train as hard as you want, but when you start to reach middle age you’ll find that regardless of how much you train those that are younger than you can’t quite keep up. Yes Vegeta is not that much older than Goku, but remember that he was already fighting Saibamen when Goku was born. BTW, this problem is compounded by all the time Goku has spent dead.
Second is that Goku is much taller and has a much bigger build than Goku. I know it’s not much when you can fly and shoot lasers out your hands, but these two are basically in different weight classes. No matter how much Ki these guys accrue Goku’s body just has that slight edge against Vegeta’s.
Vegeta is clearly better than Goku though. He has to train that much harder just to keep up. He’s a MUCH better father than Goku too, he’s clearly smarter than Goku, and there’s no doubt that Vegeta married the more beautiful (and smarter) woman. As far as Character arcs go, Vegeta actually had one. Goku’s as static as ever.