I actually think their trilogy approach with BvS and what would have been JL1 and JL2 was a problem. There are two competing parts of the strategy: have a finite story with a finite ending, and also have an extended set of solo films. I think both misread what the audience expected and wanted. If they wanted a finite, linear story, they should have just gone with it and billed it as that. If they wanted something more open-ended and long lasting like the MCU, they should have gone with that. But instead they marketed part 2 of Snyders limited five-part story as if it was Iron Man 2 leading to an actual sprawling megafranchise when it wasnt. And even with BvS they were trying to market JL as DCs answer to Avengers, when Snyders plan was for it to instead be more like ROTJ or Deathly Hallows Part 1. That created a mismatch in expectations, and it suggested even during BvS that WB didnt know what they wanted.
Its clear that, in the beginning, they wanted MOS to be the start of a Nolan-like Superman trilogy. That clearly morphed into a Superman trilogy that more or less fast-tracked to JL and Darkseid, but still Supermans trilogy, with several spin-off solo films. But if thats the approach, then you cant also try to sell the DCEU as if its also going to be like Avengers and the rest of the MCU.
Of course, I think they should have somewhat gone with the MCU approach; if not a fully interconnected storyline, then at least a movieverse built on each character getting their own solo trilogy.
Yeah, its interesting. Watchmen for example, set up a whole generation of superheroes in a single montage sequence, and in a weird way defined a whole generation/decades and we got a very clear idea of who everybody was, and what went down. Then we go straight into the main story, as we are introduced to the many characters, and we figure out who they are. I think its far more interesting when we have to fill some of the gaps ourselves, than have it all laid out. You get to know who they are through their interactions and character work.
That only makes sense if you dont care about each individual character getting their own films. But you cant both do this ensemble film, no backstory approach and also try to do the solo Batman, Superman and Wonder Woman approach.
And as for filling in the gaps, writers shouldnt need to explain everything about a character through exposition, but they most certainly have to develop everything and know everything, because thats the only way you get believable and consistent characters. And filling in the gaps only matters if you are dealing with a mystery or thriller. Plot gaps in a story (like, Lex Luthor knowing Bruce and Clarks identities, when the fact of the alter egos is central to the concept) are problematic and a sign of lazy writing.