It depends on what you accept as "proof."
Editorial comments have stated that Superman *is* the strongest hero with no physical equal. The reasoning? "Someone has to be."
Editorial has also deemed WW as the second strongest character in the DCU repeatedly and stated shes more powerful than CM.
Then you have the comics. I would guess CM & WW could perform nearly the same strength feats that Kal has. They may or may not strain more but at the end of the day the result would be the same.
CM hasnt had nearly as many appearances as WW & Superman, though. Superman & Wonder Woman aided in moving the Earth, they lifted Spectre (albeit briefly), etc. Both have had very impressive strength feats.
CM really hasnt had any major strength feats at all. He has lifted a plane (which Diana & Kal have done as well). His major 'claim to fame' is KO'ing Superman (unfair bc CM has the ability to exploit Kals weakness). In all of his fights with Superman he has lost - and at times lost badly.
Then you have all the comments about Wonder Woman being the most powerful female in the DCU. If thats the case as DC keeps stating then she is more powerful than Mary Marvel (who is equal in power to CM).
But in the end, it doesnt really matter. CM has changed and we dont know the full extent of what his powers will be.
And whoever is stronger isnt stronger by a large margin - the difference is probably so minimal that it doesnt really make much of a difference.
> I'm not asking who would win a fight but has it ever been (Post Crisis) ever been shown or stated that Superman is actually a level above WW CM or even MM ? They all seem about even in most of the stories I've seen.
> And whoever is stronger isnt stronger by a large margin - the difference is probably so minimal that it doesnt really make much of a difference.
It such a small margin that it really don't make a differents.