"Newest" superhero. To me, it's always been crucial that Superman was the first, and other superheroes came after him and most of them tried to idolize him. Realistically, Superman shouldn't be considered a surprise to people if they've already had encounters with aliens and other metahumans, plus Green Lantern which technically alien since the Green Lantern corps comes from outer space. Still, the fact that Superman is a "new" superhero and called "Superman"...well...to most average comic book movie goers don't even know that Superman was the first, particularly the ones that think Superman is lame, but it's a wonder they think the name is unoriginal when, Superman, was in fact, the original superhero.
Superman is arguably where the trend and term "superhero" came from, before the Green Hornet was even considered a superhero, he was only a crime fighter. If not for Supes, there may not have even been a Batman, and undoubtedly there would not have been a Shazam/Captain Marvel, Spider-Man and other heroes alike.
Even if Superman is not the first superhero in this movie (which I take personally moreover actually hate it) what is most important above all, I think, is that Superman has to be portrayed as the ultimate superhero. He needs to be the beacon. I'm not saying anyone has to like Superman better--to each their own--regardless of Batman's popularity, we lived in a time (starting in 2005 and 2013 onwards) where people thought the famous 'no killing' rule came from Batman, and thanks to Zack Snyder's Man of Steel, new generations were led to believe that Superman does kill, moreover never had any such morals such as the no killing ethic. That has really bothered me so much.
The fact that Batman--whether you thought of him as cooler than Supes or not--was ranked and voted as the 'best' superhero and morally superior and more ethical than Superman, was absurd. More popular, maybe, but morally superior than Superman?? Bull. $#&%. The problem with Snyder was that he only seemed to highlight Superman's physicality more than anything else--without exploring Clark's humanity, morals or ethics at all-like truth and justice. He just seemed to be portrayed as an incredibly powerful being without a specific purpose, but could cause a ton of damage and destruction.
There was a young guy I once knew who was a huge Superman fan, but didn't like Man of Steel, and debated with me that Superman actually does kills-which I said "No, he doesn't!" and he then showed me a clip on Youtube from the animated adaptation of, "Superman Vs The Elite"...but then I asked him, "Did you not watch the entire film?" He said, "No." I told him, "But Superman didn't kill them! (the Elite) That was the whole point of the story!"
Back to the subject of the new movie--out of curiosity, how long has Superman existed in this world already? It seems we were all previously led to believe it had been 2-3 years, but now it looks like he has only been a superhero for a few weeks, or a few months?? It might make sense in the case with Lex Luthor who clearly hates Superman's guts, so why would Luthor wait after so many years to try and destroy Superman's reputation and killing him.