Somebody said earlier that the jump from welter to middle seems to be larger than a corresponding leap between other divisions.

I hadn't thought about that, and I think it's a good point. Only the very best manage to hold welter and middle titles .... people like Emile Griffith, Carmen Basilio and Ray Robinson come to mind as possibly the only three who were the true undisputed world champions.

Even split title holders who have done this are an impressive bunch, Tommy Hearns, Ray Leonard, Roberto Duran, Oscar de la Hoya, Felix Trinidad and Miguel Cotto. I had to look this up, so there may be more.

Perhaps, as it is in the 'middle' 😀 Of the divisions, it tends to be a bit of a crossroads. In the olden days of 8 weight divisions with a sizeable difference between them, it was much harder to become a multiple weight champion. In more modern times, nutrition has allowed people to move weights more effectively, and perhaps people start off lighter, such as Floyd and Manny, and then move up but are too physically small to get all the way up to middle from welter. Equally, people may start off at around middle and then fill out and move up from there, such as Roy Jones, James Toney etc.

Just comparing Floyd and Manny with Roy and James seems ridiculous doesn't it?