Why do you think Krillen never became as strong as Goku even though they grew up together ?

and trained with Master Roshi together One possible reason why Krillin never became as strong as Goku is that he did not have a Saiyan tail. Goku’s tail gave him a huge power boost when it was first cut off by Roshi, and Krillin never had that advantage. Additionally, Goku was able to use the Ultra Instinct technique, which greatly increased his power.