This is just my opinion so perhaps what I'm saying here is completely just opinionated... take it as you will, but I believe Joe Lewis had more technical skill in knocking out fighters (most of his fights within round 1 or 2 people were knocked out consistently) where the Jet had much better scoring hits, but not many knockouts. He does have some fantastic spinning kick KOs or KDs though. Now, not saying knockout is the only thing that defines a fighter. Benny The Jet has nice hands but his strongest tools were his TKD and Karate base kicks. Joe Lewis has experience in Karate, boxing, and JKD in terms of striking. Lewis has better advantage because his main best tools were his hands and Lewis could box better than the Jet.
Lewis trained with Bruce Lee also gives him more of an edge. The Jet admitted recently when he was young his entire youth was spent training to climb up the ranks as a fighter to earn Bruce Lee's training, but the Jet was really young and when he did start to come up Bruce Lee had already been dead too early.