People bring up how Captain America is proof that the boy scout concept can work. Okay, but Cap works because again as you pointed out with Batman. He's essentially a regular guy with special skills, abilities(though not godlike), and people can essentially relate to him a lot easier and better than an alien with limitless power.
Cap is a walking american flag (literally) and in today's political climate that's an issue, hence why cap 1 was named the 'first avenger' overseas! The test of making Cap work IMO was much harder than making superman work yet despite of that Marvel made the character work and thrive because they didn't shy away from his inspirational good nature like I believe WB have with supes.
But even the widely revered DCAU version (which, before Snyder's was my favorite Superman) had a dark edge to him. In fact, he was at times very militant and no nonsense in the Justice League cartoon especially. He was quite different from Reeve's more "aw shucks" interpretation. So, I think this need to bring edge to Superman has been going on for a long, long time. And even then, Superman's solo animated series was nowhere near as popular as Batman's when it came out and didn't last too long. Its been a struggle to get this guy to connect with wider audiences who seem to favor heroes like Batman and Spider-man and Iron man.
BTAS was a landmark show, so just because STAS wasn't as popular doesn't mean it wasn't popular and the reason why it didn't last as long was because Timm (who prefers batman to superman) wanted to do Batman beyond instead.
As for Reeve's superman, well I suggest you go watch Donner's superman 1 and 2 and yoú'll realize Reeve's superman wasn't the "aw shucks" silver age superman you think you remember. Reeve's superman was vain, irresponsible and downright cruel throughout the 2 films i.e. NOT PERFECT. Yet he connected with the cynical audience of the 70s because Superman was allowed to be charming and likable....AND he was given dialogue to do so.
I don't think the wider audiences favor Batman, Spiderman or Ironman because if you check the numbers Man of steel opened bigger than BB, ASM and Iron (comparing origin films here) in both the domestic and international markets, which atleast tells me that the audiences want to see a good superman movie but unlike BB or Ironman and to a lesser extent ASM, MOS dropped like a rock in it's subsequent weeks due to it's divisive nature.
So, I do think its a tricky balancing act. Superman's inherent problem is that he is SUPER-man, a guy who is near invulnerable and supposed to be the ultimate altruistic individual. And I think at the core of it all, that was Snyder's ultimate intention, to make Superman relatable, to make him vulnerable physically and emotionally. In a lot of ways, I feel like he gave Superman the Spider-man treatment, made him this guy with the weight of the world on his shoulders and aspire to do the right thing only to be kicked down every time he did. The execution of said intention is, of course, what we debate about these movies, but I think Snyder ultimately was trying to bring this guy down to earth to our level so we can relate and sympathize with him.
Have to disagree with you there, superman's inherent problem is that he's been handled by a studio and a bunch of directors (singer then snyder) who were ashamed of his nature and thus tried to bastardize him into something he isn't and before you say that Singer's superman was the same as donner's I advice you to torture yourself abit and actually watch SR again and you'll realize how mopey, emo, creepy and dialogue challenged superman was in that movie.
Superman was created out of wish fulfillment, to be the dream and the dreamer and when ever someone tries to make him
'relateable' (what ever the hell that means) they end up failing. Superman I believe is meant to be
likable not relatable and inorder to do that he can't spend large portions of time in his movies moping and spewing out pieces of dialogue like "no one can stay good in this world", not when Snyder and co. spent alot of time in MOS trying to
tell us how Superman is
meant to be the embodiment of hope.
I see people all the time saying how superman doesn't work for the modern times but until the day comes when a
good superman movie is made and people still don't show up then I will continue to believe that all the character needs is to be handled by someone who actually respects it.