It's no secret that the DCEU didn't get off to the best start. While the casting was spot on and the budgets were generous, the film franchise struggled to find its groove with mainstream audiences in the same way as the MCU had. Whether it be a tonal issue or the incompetent meddling of executive suits, the DCEU - as of this writing - hasn't even matched its DC franchise counterpart in the Arrowverse.
The Arrowverse television shows may have small budgets and built around classic CW drama, but what it lacks in cinematic and bombastic presentation, it more than makes up for by wearing its heart on it sleeve. The love and respect that (most) of the characters receive in the Arrowverse have led to its popularity, unabashed to represent its comic book source material for what it is, whether it be beyond cheesy or as dark as the lighting in Game of Thrones.
The steps that the Arrowverse has taken have led the way for both the DCEU and the MCU, whether it be the construction of appropriate tones for the respective character, or pushing the limits for what a mainstream crossover can be.
7. Slow Build Of Characters
The Arrowverse wasn't always the pantheon of heroes and TV shows that it is today. In the ancient world of 2012, there was only one show by the name of Arrow. The show was dark and gritty and very much isolated within itself, until half way through the second season, where Barry Allen guest starred. Throughout this season, Arrow also implemented an Arc Motif whereby TV presenters or side characters would mention Central City's Particle Accelerator. These hints and build towards the Flash series created a smooth transition that made the world building feel organic.
The Arrowverse then took another break, letting the Flash's first season some space to evolve and fully integrate, before introducing the Legends of Tomorrow - a team of the latter's side characters. Supergirl also began in the same year, which was a happy accident for the CW after CBS passed on a second season.
This slow build of characters fleshed out the Arrowverse in ways that the DCEU hasn't yet. Introducing a whole Justice League before you can meet them individually takes away from their interactions with one another. Sure, some of these encounters in Justice League were fun, but it's hard to know who the characters are when you haven't seen how they operate individually.