Some thoughts on Earth-2 Superman.

[Gernot]

It doesn't work out that way ALL the time, though.  

Captain Marvel had gone to Earth-2 during World War II, and defeated Superman in closed combat.  

I seriously doubt Superman could have defeated Captain Marvel on another Earth.  Marvel's magically-based strength was greater than Superman's, at least during that point in the heroes' lives.

[Captain Kal]

As of November-December 1977 in Superman Family #186, E-2 Superman was still being portrayed as E-1 Superman's equal (Battle with Krogg).  That's decades after "Negative Crisis on Earths One/Two" for that JLA/JSA team-up.

It wouldn't be until 1980 or so under Wolfman that E-2 Superman would start being portrayed as weaker than his counterpart.  Even then, it was not that dramatic a difference as Wolfman scripted Kal-L knocking out Kal-El in COIE.  He also dealt the final blow to the Anti-Monitor, thus giving a figurative and literal closure to the Pre Crisis era -- the super-hero who started it all is the same guy who closed that era.