The Daizenshuu entry of him being at 23k makes the most sense. It's not until after Vegeta's battle power is read as 24k that Dodoria and Zarbon comment on him being above their power, implying that they're not inferior to 22k. Kuririn also held some hope in Vegeta and Zarbon being able to take each other out, suggesting they were comparable. Zarbon's performance was mainly down to his rusty fighting skills from being complacent with his power, as well as perhaps a drop in shouki or yuuki from learning Vegeta killed Dodoria.