I think it should count maybe from the first title so when Tyson beat Berbick... just seems more fair, so then Tyson would drop off the list if it was that criteria
1. Jack Johnson 2. Joe Louis 3. Mike Tyson 4. Jack Dempsey 5. Sonny Liston 6. Joe Walcott Another name I am going to throw out there is Jack Sharkey. Wladamir Klitschko is in the argument, if you consider fights up to the point where he was considered lineal.
Lennox Lewis is another messy one due to alphabets. We could say anything prior to 1993. Or before he beat Shannon Briggs (who some claim was still linear) 1998. Or before he beat Holyfield in 1999. Under the latter two standards, yes he's a good call. Under the first option, not so much.