This is a notion that I just don't understand (and I'm not singling you out, a-dev, as your thoughts on this are absolutely among the majority.
But here's the deal: The Marvel Studios way of building their cinematic universe WAS perfect. FOR THEM. But it need not be a blue print for the only way to do so. People often overlook the reason why Marvel took a slower, methodical approach to introducing each Avenger character: They basically had to. It might be hard for some people to believe now, but before 2008 Iron Man was NOT exactly a household name. To say nothing of a character like Black Widow.
The main difference is that Warner Bros/DC doesn't really need to introduce the core Justice League characters to the world. Everyone is already familiar with them. And not just Batman, Superman and Wonder Woman (who pretty much any human in the civilized world is familiar with)... even their 2nd tier characters (Flash, Aquaman, etc) are pretty well known. So there was no need to do several solo films before bringing them all together. All they had to do was introduce a movie universe that they could all share and inhabit, and then get on with it. And that's exactly what they did. Whether or not it will work will remain to be seen over the next couple of years, but clearly WB felt that this was the best way to build THEIR cinematic universe. And I personally tend to agree. This is not a Zero Sum game. It's also not a race, despite how the internet wants to see it.