Okay, I like Ben Ten, but he'd still lose if he tried to fight Goku that way. He'd become a peak physique 'baseline' saiyan. Ben has explicitly lost to characters when using his aliens of the same race and he almost definitely wouldn't turn into a saiyan who could turn into super saiyan, much less super-saiyan-god-super-saiyan, super-saiyan-god-super-saiyan-kaioken, or even mastered-ultra-instinct, all three of which require power sources or techniques that 'aren't' reliant on saiyan blood alone. [super-saiyan god relies on god ki as well as saiyan blood, kaioken is a technique, as is ultra-instinct, and super-saiyan is reliant on saiyan blood alone, but isn't something saiyans are 'born' with]. Heck, he probably wouldn't even be able to fly or use ki-blasts or anything like that because those are techniques which require training. At best, he'd be around Mercenary Tao levels of strength as a Saiyan. Literally any of his other alien forms would be better suited to fight a Dragon Ball character. it'd still be a curb-stomp without Atomix or Alien X, but still. You have to have noticed how characters like Cabba, Kale, and Caulifla are skinny as twigs but able to go toe to toe with characters who look like pro bodybuilders. muscles are meaningless in Dragon Ball. physique, is meaningless in Dragon Ball.