Schmeling was still a former LHW who won the HW title. The fact is many great or future greats who started at LHW either never fought for or won the title...so I don't see why Spinks is the measuring stick. He was just The first who won the title to do it..but there had been many LHWs before him who won the HW title.
The cruiser division put a 25 pound barrier. But we still had 4 former LHWs in Recent decades win HW titles in Holy, Moorer, Jones, Toney
I think that to qualify for practical purposes, you have to have had some sort of world level career at light heavyweight. Otherwise we could call Gerry C00ney a former light heavy.
Than we can still include Braddock, Charles, Tunney, and arguably Bivins before Spinks. And Patterson. This is at least one per decade from 20s to 60s. Than Spinks in the 80s. So 70s is the only exception.
Taking them in turn: Braddock was a world class light heavy, but he had his chance at the title, and came up short. This means that he was world class in both divisions, but only closed the distance in one. Tunney and Charles might very well have held the light heavyweight title, had they been given the chance to fight for it. I don't think that Joe Louis would have tolerated Bivins holding the heavyweight title, but Billy Conn came shockingly close to turning the trick.
Again, that means we've had a former world class LHW claim a HW title in every decade since the 20s..bar the 70s. I would say they've done well.
I am with you on that, but it is interesting that this gap is seldom closed (lineal to lineal). We waited a long time to see a heavyweight reclaim the lineal title. This is interesting.
The LHW division has produced some of the more historical lame duck lineal Champs. So it's not surprising these guys didn't became two divisional champs or even try. When we think of the LHW greats.. so few won the title. Most of the best ones got more opportunities at titles or money fights north of 175, and took them.