I think there is a difference in spectrum of tone as opposed to characters not fitting an appropriate tone.Shazam is the outlier, not the norm. Its a goofy film that subverted the character from anyone who ever read the Fawcett or various DC comics. To the uninitiated, he was just silly.
The MCU is just as "all over the place" with lightweight films such as the stumbling-over-itself-to-be-funny Thor: Ragnarok, the Ant-Man and GOTG films, which are the polar opposite of the Captain America films, The Incredible Hulk, Black Panther, and at least half of the Avengers movies. The MCU is far from having a consistent tone, and the best movies in that franchise are the darker films.
The DCEU was consistent and successful with the superior entries in the line: MoS, BvS and Wonder Woman. That is a film universe with its own voice, not trying to be a wrongheaded "comedy in tights," or as lightweight as certain superhero TV series.
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So I think Thor and ANt Man wouldn't be a s fun if they were as serious as Black Panther and Captain America. Or, even moreso, many people would have hated Black Panther and Captain America had they had the same tone as Thor Ragnarok or ANt Man or Guardians of the Galaxy.
I grew up enjoying Ambush Bug and the Keith Giffen Justice League International, with Crisis on Infinite Earths & New Teen Titans in between. Huge tonal range...but they were ALL a part of the same DC Universe I enjoyed. Had Teen Titans played like Ambush Bug (or the Teen Titans Go of today), I would've hated it... but it was great for the characters and how they were treated.
Though I think GotG2 and Rangnarok were at times a bit over the top...it still felt a part of the same universe.
I think the other thing @Christopher pointed out was the inconsistency of how Superman was portrayed... as a menace the first 2 films, to a beloved hero that everyone mourned in Justice League. That just didn't seemed to vibe... I mean a Captain America montage of the in-between years (where Cap went from mascot to bona-fide hero and leader) would've have helped that make sense.
Snyder cast them, and as head director and producer, he was the fighter in their corner. Without him or someone to replace him, these are the consequences.
Gadot has Patty, the MCU has Feige, Jackman had Mangold, Reynolds had Jackman to back him for Deadpool solos, DCTV has Guggenheim and Berlanti, Mission Impossible has Tom Cruise, Fast and the Furious has Vin Diesel, etc. Superman is a lot like Star Trek on film now. Nobody wants to touch it and stay. It's a valuable IP, but not many people are volunteering to tackle the project.
Even when Snyder was there, WB couldn't nail down directors for all movies on their slate. Idk what direction they're moving in now. It's a shame to see so much talent walk out and potential stories left untold.
The thing is Geoff Johns was supposed to be that for the DC FU....but Snyder seemed to ignore him/ not have a working relationship with him (as opposed to Patty Jenkins, who seemed to work really well with Johns)
Well, for me, it was specifically CHALLENGE of the Super Friends that I really really liked. (and that one episode where Superman switched places with his evil self).It seemed to be the only way Shazam was produced.
Some (not meaning you) have this long-disproven fantasy that DC was the equivalent of Archie comics, when the source--the comics--have not seen any treatment like that (with most of its mainstream characters) since the mid-late 1960s. This desire for DC movies to embrace that silly direction also reads like people who thought the horrid Super Friends cartoons was the "true" DC, despite the fact the comics were the polar opposite of that all along. No one is going to take a DC film seriously if it comes off like the aforementioned Super Friends...or the George Reeves Adventures of Superman, West Batman or Carter Wonder Woman. Audiences do want to see how fantastic characters would look in a more realistic environment, but that cannot be achieved with a two hour tribute to quips and Saturday morning action.
What I think many fans would like is a movie that respects previous adaptations , and evokes some of those fond memories, while being it's own thing. I think the Raimi SPiderman movies and DCTV's Flash do that -- and thus helped with the popularity of those.
Flash and Supergirl have used actors from previous incarnations , and did so in a smart way, so that those characters were embraced, while still allowed to be its own thing.
I'm talking about the MCU in general, and overall they've managed to find a good balance between the darker and lighter elements. Some movies do go more in one direction or the other, but overall as a franchise it's in a pretty good middle place.
Sure Thor might have ended up comic relief in Endgame, but the rest of the movie is definitely darker than a lot of the MCU movies have been. Overall Endgame is one of the best when it comes when it comes to balancing the lighter and darker moments.
If the movies are built from the ground up with this kind of tone in mind, then I don't see how that would be a problem. The only time they come off disjointed is when they've gone back in later to try to change the tone.
You say that like it's a bad thing. The changes made to Thor from Ragnarok on are the best thing to happen to the character yet. Endgame did take things to a temporary extreme with how he handled the post-Snape world, but they had already toned it back down to where it was before the Snap by the end of the movie.