BvS is no more ambitious than anything Marvel has put out . You can laugh at the tone of Guardians of the Galaxy, but the decision to throw those characters on the screen with that budget, in that setting, was way more ambitious and riskier from a studio perspective than deciding to throw Batman, Superman, Wonder Woman, Lex Luthor, Doomsday, The Flash, and Aquaman on a screen.
Everything you brought up; accountability and whatnot wasn't explored in any real substantive way, no truly unique or clever angle was explored, they just presented the common talking points of the subject and scowled at each other instead of having a thought out conversation without a clear winner. I mean, did Wonder Woman even say one word to Superman in the entire movie?
Drowning a film in dour music and a blue and grey color filter simply presents the illusion of taking a subject serious, but it's all undermined by CG monsters, stupid plot solutions, fake deaths, and hollow character moments. A 3 hour release would have been slightly more ambitious and certainly a bigger risk, considering it would have meant fewer screens, but ultimately the film was just an on the surface exploration of it's themes, no matter how many times people say it's deeper than the average comic book movie. No, it's just as silly, just as reliant on action, just as reliant on one note mustache twirling villains, but it's also presented as if it's better than that, which is why it gets laughed at instead of tolerated.