Does it annoy or bother you when people. Make fantasy match up threads between light heavy weights and heavyweights ? For example Kovalev vs Povetkin ?
All 'fantasy' match up threads are pointless. Different weight classes in the same era, are just as pointless as the same weight class (e.g. Ali vs Joshua) in a different era.
Could Roy Jones Jr. win a heavyweight title? What kind of success would Adamek have at heavyweight etc.? LHWs move to heavyweight from time to time so evaluate if one has sufficient skills is not really annoying.
Knowing that some of the light Heavyweights nowadays are heavier on fightnight as some of the 60's and early 70's "heavyweight" contenders, I don't think it's such an issue.