13 defenses, a record unmatched until Joe Louis came along some 26 years later. Hardly the worst as a champ
After a couple extremely soft touches (James Walker (1W-5L), Jim O'Brien (0W-1L)), a couple wins against decent undersized guys he reverted to barnstorming and playing keep away from Johnson. By those standards Sullivan had hundreds of title defenses. I have always given him credit to ultimately facing Jack but he was nothing more than a placeholder.
As a champ, he was still better than Marvin Hart, Primo Canera, and Jimmy Braddock. Undersized but not compared to himself, managing such a high activity rate during his short reign is noteworthy, even if the majority of his opponents weren't great