I’m probably way off but I’m going to guess light heavy. That title has changed a lot of hands. Be interesting to see what someone who knows better comes up with. It can’t be heavyweight due to several of the long reigns of men like Sullivan, Jeffries, Louis, Ali, Holmes and Klitschko
HW should have Cardiff, Killen, McAuliffe, Peter Jackson and possibly Archie Moore added to the lineal title ranks.
Cardiff should have taken the lineage from Sullivan. It was a draw but clearly Cardiff won even if it was due to injury Sullivan did not fight in gloved boxing for 5 years. In terms of Moore it'd be beating Parker after Marciano was retired.
Number of lineal champions: HW = 38 LHW = 36 MW = 43 WW = 69 LW = 43 FW = 44 BW = 48 Fly = 45 I've not checked the inbetween super/junior divisions, but I can't imagine any will have had more than the 69 lineal champions that there was been at Welterweight.