>The fact that people are saying this - "DC is the underdog" - is a true testament to how thoroughly the DCEU has shit the bed with the lights on.
The individual properties involved in each cinematic universe would make any gambler with no knowledge of the films, but all the data of character popularity in comics and movies for the past fifty years, bet all of their money on DC.
On one side you have three of the four most iconic superheroes ever, Superman, Batman, and Wonder Woman, not including Marvel's Spider-Man. Additionally, you have the rest of the Justice League, which as a group has comparable brand name recognition to Wonder Woman.
You also have both of the most well known and probably the objectively best villains in comics, Lex Luthor and the Joker.
You ALSO have any and all of the supporting characters for those heroes and/or villains, including Alfred, Robin, Lois Lane, Jimmy Olsen, Harley Quinn, the list goes on and on.
YOU ALSO have a closely analogous universe to our own with two made-up cities - Gotham and Metropolis - that are literally, not figuratively, more household names than real cities in America like Des Moines or Baton Rouge.
And then...on the other side...you have the Avengers, the figurative cold-storage locker for third string Marvel properties that weren't able to make it into their better franchises. The MCEU is and has been the low-recognition properties given to Feige because the X-men, Fantastic 4, and Spider-Man (at the time) had better things to do with their time.
So you had an unstoppable juggernaut of brand loyalty and awareness against a rookie lineup with both hands and a foot tied behind its back, and no matter how Marvel did, no matter how many supposed shillforce alpha teams went undercover on RT, it was DC's fight to lose.