I don't know what they expected him to say. Snyder is the one who cast him. Kind of like how people acted like it was a surprise that Snyder's son thought that his dad's version would be better.
https://heroichollywood.com/ezra-miller-zack-snyder-dc/
How was it fine? It basically caused the fandom to be split in half where they are still arguing how good/bad the movie was years later. For a first movie that is supposed to kick start your movie universe divisive is not what you want. It is the last thing. It caused them to stumble out of the gate. You want a movie that appeals to the general audience where they can buy into the world and more importantly the character so they feel invested. Then you can take that goodwill you built up in the first movie and can try something more challenging/unexpected in the second if you want. That is what Nolan did with his Batman movies.
Plus some nonsensical characterization. Batman thinks of his dead mother and suddenly all the reasons he had for hating Superman are gone and they are friends (he actually introduces himself as "a friend of your son" when he saves Superman's mom). No true resolution to any of their issues (which I thought were forced in the first place).
That's also very puzzling. Why combine two stories so thematically different? Two stories that each one would need a whole movie to fully breathe? And two stories that work better when they take place down the road for both heroes and not so early on?
Marvel really just did simple things. First introduced the characters in solo adventures before the team up, just like it happened in the comics. Did Civil War only after the heroes had some adventures under their belts. And no weird mashups like "Let's do Civil War and the Kree-Skrull War in one film".
Taking into account that modern superhero movies started around 2000, and that WB have always owned all the characters and have always had the capability of making their own movies, Justice League is more like 12 years too late.
If WB had any sense or capability they could have gotten a DC Cinematic Universe up and running long before Marvel even got into the game. Instead they sat on their ass and then finally released Batman Begins in 2005 when they should have had a bunch of movies out already by then and instead could have been releasing Justice League.
The thing is that it was WB's vision, that's why they hired Zack. They saw TDK Trilogy, and thought that should be the direction for their next set of DC movies. Zack's sensibilities fit.
I personally give MoS an 8-8.5/10. Theres missteps in the storytelling, but it's more than good enough.
There's nothing wrong with MoS, but the tone, and direction, was not widely accepted. It was more to do with how Superman "should" be represented.
Honestly, its looking like Superman is lose-lose. I think that's why Shazam is being pushed.