A: Clark in BvS isn't played to be purposefully dour, straight, and serious, but in how his character understood the gravitas of the situation and contemplated whether what he was doing was beneficial to the world overall. There are actually more moments of levity but they involve Clark's interactions with Perry (and how Perry responds to him being absent so often), but you said it yourself: Reeve's Superman would not make sense in Snyder's interpretation, but I would argue that making Clark light-hearted and goofy would only undermine the seriousness of the situation at hand. When Clark first sees Lois in the bathtub, he wants to be all smiles and kind, but Lois brings him down to the ground with the fact that hearings have started.
B: The impact and destruction of both Smallville and Metropolis worked to serve two purposes - That a fight between multiple super-powered beings would cause a lot of collateral damage, showing the consequences of such actions, and realizing that Clark had little to no idea of how much damage he was capable of. His initial fight with the two Kryptonians was his first time getting into such a large scale fight, and there were many moments from the both of them shoving or hitting each other into buildings due to the impact of their punches. He punches Nam-Ek into a train station with oil tankers so you could potentially infer that it was devoid of people at the time. Ultimately, it was Superman's first fight and he was in many ways out of his depth to be able to dispatch his opponents to somewhere less occupied. Zack Snyder wants to show the destruction because that's how it would have looked in a real fight, and doesn't want to shy away from the potential loss of property and life.
C: I would have loved your story beat when I first watched BvS. Of course I wanted Superman to deliver his speech, to explain why he can be accountable and why he wanted to help out people the way he does. That's why it's such a gut punch when the explosion happens and he's essentially led to the death of dozens of innocent people simply due to his presence being there, and him still being able to witness it all. In the Ultimate Cut he is shown delivering survivors to the emergency team outside, but overall the story wouldn't have been served because this is, quite simply, the worst he's being painted to the public in the entire movie. That he unwittingly was the target of a bombing and that his being there is, in terms of story structure, the lowest point of the movie.
D: And I would tell you that many people do resonate with this version of Superman. At the very least, MoS and BvS made me care about the character a way the comics, TV shows, and animated cartoons never made me did. There's no end to the people on Twitter and outside the greater wide world who are inspired by Snyder's interpretation (they're there if you look).
E: Cap's lack of contemplating the ramifications of his actions are apparent in Winter Soldier and Civil War. Risking SHIELD agent lives on board the ship. Risking innocent lives getting caught in the crossfire during his first fight with the Winter Soldier (he could have just detained or killed him). Compromising his effort when he realized the Soldier was Bucky. No thoughts on him regarding the damage done to Washington D.C. during the third act. Compromising himself again when Rumlow talks about Bucky. Not telling Stark that HYDRA was responsible for the deaths of his parents. Getting indignant about the Sokovia Accords all because Sharon delivered a eulogy at her Aunt's funeral. Not wanting to talk it out at the airport. And finally potentially making his new refuge at the end of Civil War a target for government agents out to apprehend him. As much as I love Cap from the comics (OK maybe not as of late
), his character arc in the films has only gotten less and less ideal and adherent to his principles.
F: "There's not a single moment in MOS where Superman reflects on the mass-scale collateral damage and the innocents caught int the cross-fire". He cries and clings to Lois after he kills Zod. I'm not a fan of the next scene where he seems composed, but that's probably the one thing I can agree with you on there.
Man I love talking about the stuff in the DCEU films. Continue on, my good man Dragonyeuw!