The two aren't mutually exclusive. Although Zab converted to Christianity some years back From Wiki: Judah's father is an avowed Black Hebrew Israelite and Judah's family has declared themselves Jewish.[52][53] Judah thanked "his Lord and Savior Jesus Christ" after his 2005 fight against Spinks.[54] Zab is now a Born again Christian.
Leonard beat the best comp in lightweight history, and by all accounts could box, fight with power and was top notch defensively. The film we do have him shows him gliding smoothly in the ring and that is with old black and white flicker film from a distance. Leonard also ranks higher on most p4p all time lists though that is subjective. All that said, Ross is still my favorite jewish fighter. From his humble beginnings to the murder of his father to his association to Al Capone, to the great fighters he fought and on to him being a war hero and developing a morphine addiction due to his injuries in WWII and overcoming it only to speak out against addiction during a time it was taboo, the guy has a legendary story.
Benny Leonard and Barney Ross being the most famous Jews in the sport but you also have Brits like Ted Kid Lewis and Jack Kid Berg who were Jews. Battling Lavinsky, Abe Attel and Max Baer were other great Jewish boxers.