Martial characters really need epic destinies. I think it's that simple. Casters don't really need them because being a level 20 wizard or cleric already is one.
But I really think the simplest thing would be a tier system. The game just needs to decide at which point a Fighter goes beyond say Conan, and give a fictional explanation of this. It could really be anything, it could be they are on the path to becoming a demigod and so no longer age, are immune to disease, and explicitly and fictionally can break the laws of physics in certain domains. As always people will insist that this is unnecessary, but I just don't see any way forward without this concession. As long the vagueness remains the arguments will continue.
Ultimately however, it is impossible to resolve anything without doing something with the implied setting of the game. That's why I think putting characters on the path to godhood is probably the simplest solution since the idea of mortals rising to gods is already a long standing background element of D&D.
But I really think the simplest thing would be a tier system. The game just needs to decide at which point a Fighter goes beyond say Conan, and give a fictional explanation of this. It could really be anything, it could be they are on the path to becoming a demigod and so no longer age, are immune to disease, and explicitly and fictionally can break the laws of physics in certain domains. As always people will insist that this is unnecessary, but I just don't see any way forward without this concession. As long the vagueness remains the arguments will continue.
Ultimately however, it is impossible to resolve anything without doing something with the implied setting of the game. That's why I think putting characters on the path to godhood is probably the simplest solution since the idea of mortals rising to gods is already a long standing background element of D&D.