This is untrue/inaccurate. The announcement that the MoS follow up would have featured Batman and Superman was made only 4 weeks after the MoS release and included a BvS logo reveal. That alone suggests the movie was already in advanced development at that point. The project started during the post-production of MoS, after they were discussing a potential antagonist for the sequel and Snyder suggested BM.
From Jay Oliva: "Back in April 2013 (before MoS released in June) I was tasked with doing the Superman 75 short. I met with Zack who was the exec producer on it and he showed me storyboards of BvS with Batman already in it. AND it was a Batman from DKR. I know this as fact because I was there and I remember it very clearly because I was sad that I may not get the opportunity to work on a film that used Miller’s DKR as an influence. Because well you know, I kinda did a little film that did just that. So how could it be revisionist history if the plan for the following films were already planned BEFORE the release the MoS? Now was there a plan to do a sequel when Goyer and Nolan wrote it? I don’t know for sure but you can bet your ass that prior to June there was a plan"
https://twitter.com/jayoliva1/status/987930376965210113
Also, a day before MoS release, David S. Goyer hinted at BvS/JL in an interview and BM entering into the picture because of the collateral damage at the end of MoS: "Well, yes… there’s definitely… I don’t want to get too in depth. Obviously, Zack and I have had conversations… but there would be a cause and effect. And that would extend to the collateral damage that happened, and to what other countries feel about the fact Superman calls America his home. Man of Steel doesn’t exist in a vaccum."
https://collider.com/man-of-steel-ju...e-david-goyer/