I'm sure that someone had said exact same thing about making everything darker, but it happened many times.
MCU is also sometimes criticized for having a house style with every second character throwing snarky one-liners. And DC movies have been criticized for not having enough jokes. So no, I wouldn't be surprised at all if Gunn attempts to inject his brand of comedy (as far as ratings allow obviously) into all future DC projects. And I'll be pleasantly surprised if it doesn't happen.