So Wonder Woman certainly doesnt fit in this category. When she was first made she was a lump of clay brought to life by Zeus to be his daughter. Her weaknesses included that if she is ever tied up by a man she cannot escape. Yes really.
Wonder Woman became a character lauded by women, but it certainly didnt start that way. Now along the way things have happened including Wonder Woman killing a villain and being morally unaccepted by the other heroes for doing it. She's also fought the Gods. So shes turned against her creators and who people pray to. So shes certainly not a clean cut moral brightspot
Superman does kind of fit some of it. The part that does is that he's an outsider, an alien who comes to represent the best of humanity. So the idea is that he's a really good human being, despite not being a human. So obviously morally he has to usually be right else he cant be that. However, contrary to what plenty of people believe Superman has weaknesses. Here's one of them, birthing an entirely new Justice League team led by John Constantine and Zatanna to take on mystical threats and firstly Enchantress here, who just beat the entire Justice League including Superman... Because... Superman's actual weakness is magic.
This is something you usually see from Mr. M...some other letters, in the comics. A magical 5th dimension imp that messes with superman's life for fun. But magic in general hurts him. Thats his weakness and its a big one. Another character who has fought the Justice League is Black Adam... once again magic based. He held his own.
Anyway, this is another reason why Superman needs the normal Justice League. Wonder Woman has a basis mystic ways and magical items, Aquaman some magical items, Shazam (Original Captain Marvel) has been on the team and when Wonder Woman doesnt know enough they generally consult with Zatanna or Dr. Fate who have also teamed with them.
Superman turning evil has also been done a bunch, although if its in the main continuity its an alternative version of Superman from another universe. The Injustice games were based on that story too. So there are evil and morally grey superman, just not the main ones in the main universe. And yes I say main ones because there have actually been 2 different Clark Kent Supermans.
Batman is someone who treads the line with morality. He usually stays on the right of it, but his main weakness other than not having meta powers in a world with meta powers like Superman etc is... His paranoia and distrust. This has led to several times where backup plans Batman has devised in case he ever needs to fight Superman and the rest of the Justice League fall into the hands of villains who use them to defeat the people they were meant for. On top of that there are other things like... Creating Robins. He's sending teenagers out at night in brightly coloured uniforms to be targets so he can attack from the shadows. He's using them as child soldiers. Even if he is in complete control and nobody got hurt its still wrong. And Robins have died before so he doesnt even do that right.
So thats the big 3 and only Superman has any truth to what you suggested. Moreover there are other characters like John Constantine or Black Adam who are indredibly flawed. Constantine will essentially do whatever it takes to win and have the good guys survive, so his friends and other innocent people might be sacrificed and tricked along the way to get it done. Black Adam generally only cares about his own country and doesnt care about morality outside of that. So you have loads of far more complex characters, we just havent seen too much of those ones in the movies because they chose other projects. But we have in Suicide Squad and Peacemaker, and Black Adam is next up
