Outside of Master Roshi the humans were usually pretty good in their debut arc and fall behind after that.
Yamcha: After his debut arc match he loses to Jackie Chun, Tenshinan, and Kami in the tournaments. Beats The Invisible Man in the RRA arc, but then is losing to The Mummy until Goku embarrassingly has to one-shot The Mummy for him.
Kuririn: After his debut arc he helps out during the cave segment in the RRA arc, but doesn't take out General Blue and then loses again to Dracula. Beats Chiaotzu in the 22nd Budokai arc, but then he literally dies at the beginning of the King Piccolo arc and loses first round in the 23rd Budokai arc.
Tenshinan: After his debut arc he fails to mafuba King Piccolo, then loses to his henchmen and has to be saved by Goku. Later saves Goku from a blast but then is also turned into a hostage by King Piccolo. In the 23rd Budokai he beats Mercenary Tao, a villain Goku already beat. Also, he got Talk No Jutsu'd by Jackie Chun.
Chiaotzu: Loses to Kuririn, dies in King Piccolo arc, and loses to Tao before the 23rd Budokai even begins.
Yajirobe: Good in his debut arc, but by the 23rd Budokai he went from being on par with Goku to being arguably weaker than Yamcha.
They have their moments in the tournaments, but most of the actual villain stuff is just Goku doing work.