If anything, a separate series of Marvel Zombies films / episodes would be a great palette cleanser for fans who need a break from the universe at large, giving them something fun and easy to jump into without needing to refresh their Marvel knowledge base.
Even better, those same reasons would help attract those that have purposely avoided Marvel Studios’ films, making Marvel Zombies a project that could unite the divide between those who buy into the MCU, and those who actively throw shade its way.
Most importantly, there seems to be an attitude that the success of the more R-rated material has spurred on among film and TV viewers: not everything has to be part of a cinematic universe.
While the MCU is an interesting animal to consider, as its various intricacies make it a centerpiece of continuity, not every property needs to be spun off into a universe of its own.