Why did Frieza use the Saiyans as henchmen when they were so weak?

Before Vegeta is even at his strongest on Namek and Goku hasn’t arrived on Namek, just from his Earth Zenkai boost, Vegeta becomes the strongest Saiyan any of the henchmen have seen. They were amazed how a Saiyan could be that strong.
But relative to the other henchmen, the strongest Saiyan at those moments is still much weaker than most of the henchmen we see. Vegeta has killed off many henchmen and the Ginyu Force wasn’t worried about Vegeta. Recoome wasn’t taking Vegeta seriously.
Then Namek, Goku becomes the strongest when he goes SSJ and even in his base before that, Goku is the 1st character to damage Frieza in his final form.