DC have been screwing up their movies long before Henry Cavill was Superman. Any exec that things he's to blame is a fool. Not talking about how movies bank but rather quality, Suicide Squad was a hot mess and Cavill was nowhere near that. In fact, his character was dead. The issue with the DCEU is the impatience they have in rushing through as many properties as they can and trying to hit ideas before Marvel does. Marvel spent years on origin movies, starting with three characters and slowly making it bigger. DCEU needs to scale back and do the same. We should've met Superman, Batman and Wonder Woman and then the world should have developed around them until it could stand on its own and there was outcry for spinoffs. Instead, we got a Superman movie, a Superman movie that didn't know it was a Batman movie, and Suicide Squad.
Also, even if they did believe Cavill played a role, I hope they fired their casting department. It was literally their job to find a leading man. I believe they did a good job, but if DC doesn't have faith in them anymore then they clearly aren't meeting expectation.
I've enjoyed the movies for what they were, even the hottest mess of all that is Suicide Squad, but they're shallow and inconsistent for the most part. An extended universe can't be built upon such shaky foundations, in my opinion.