Notes

We don't really know saitama's full potential yet, on other hand, is a very powerful person since he could destroy planets and destroy 1/3 of king kai's planet. But we do know that Goku's power is limited, but, he keeps transforming into something more powerful, which pretty much makes him pretty much limitless. It all depends on who keeps training and who becomes more powerful. But, like i said we don't know saitama's full potential since all we know about him is that he's human with powers that could destroy planets and withstand a black hole effortlessly. Saitama is a broken character in the anime world since he just keeps getting more powerful and powerful. If goku could withstand saitama's punches then saitama would just throw in a more powerful punch, then another powerful one that surpasses the other one, and then on and on until goku transform in his most current powerful form and defeat him. His power is limitless which means that his power is infinite, infinite means that his power is forever rising. He could literally throw a punch that could destroy our solar system and if that doesn't entertain him, then he could just throw a punch that could destroy a galaxy, then a punch that could destroy the whole universe and on and on, but we don't know that because he's never done it, because he's never faced anyone with power that could withstand him and has to destroy the universe in order to defeat the enemy. Anyway, saitama's power is infinite, and goku has to break HIS limits to keep up with him. Eventually goku can't transform into something more powerful than all his other forms until he goes somewhere he's never gone before and learn new powers. Saitama on the other hand, doesn't need to travel places to learn other martial arts or techniques or whatever because his power is forever rising. If saitama did learn new techniques and martial arts that he doesn't know a thing about, it wouldn't matter cause his power is just going forever and ever and it's not gonna stop. It just makes him smarter and a better fighter that he is right now, it's like fighting a boss in a game, you see his HP bar and your fighting with all you've got and you see his HP bar going down normally right? then eventually you see his HP bar regenerating and it's regenerating so fast that your attacks can't keep up with the regeneration and your attacks doesn't do damage to him anymore and his HP bar stays full. Saitama is like that, we have no idea what his full power is and we don't know how fast he is or whatever. And how do you know that he doesn't have a hidden transformation hiding inside him? He doesn't even know how he got his powers, he thinks he got it from the training he did (100 push ups, sit ups, and 10k runs) but we don't know that, he might have gotten his power from a god or something and blessed him with transformation that makes him faster and whatever there is, we don't know the truth about how he got his powers, we also don't know how fast he is, he could faster than he is right now, Goku has to break his limits in order to be on par with saitama. I could go on and on about reasons why saitama has unlimited powers and whatever, faster, durability and all the other reasons.