This is subjective, and it's clear that there's tons of fans out there who strongly prefer Snyder's vision of these characters. However, if the goal is to do business that equates to Infinity War level box office receipts, then yes, Snyder's approach to these films is not going to get there. In order to do Avengers box office numbers you need a film that appeals to the lowest common denominator, thus making the films accessible to as many people as possible. The violent and brooding nature of Snyder's work is for sure going to be off-putting to a large percentage of children, women, and soyboys.
There's really no reason that every character needs it's own movie to set the ground for a Justice League film. "Marvel did it" isn't evidence that a Justice League movie can't be done without everybody having to watch an 3 hour movie on each Aquaman, Flash and Cyborg. Snyder's version of Justice League went much further into the history of the characters that were introduced in the movie (just look at the trailer) and will hopefully do a much better job of making the film feel like an earned experience for each of the characters.
Also worth pointing out that it isn't Snyder making the call on what films are going into production, that's up to the studio. Snyder's job is to take the studio directives and do the best he can to work that into his film.
You understand that directing animation is a completely different skillset than directing films? Snyder is a very accomplished film director and has a very passionate following of fans. Regardless of how things play out with DC, he's going to be more than fine going forward.