This is what happened: Snyder started shooting JL before BvS came out. After the critical and commercial reception, WB got worried about JL. Snyder was pretty much done shooting everything when it was decided to bring in Wheedon. Wheedon shot mostly new footage for the 2hr movie because WB didn't want it to be so dark. They also didn't move the release date because they wanted to get a bonus that year. That's why we get Superman with horrible CGI lip, he was shooting Mission Impossible and Paramount didn't want him to shave his mustache. Snyder has mentioned several things from the theatrical cut he never put in, things like that Russian family and also having Flash fall on WWs cleevage were all added by pervo Wheedon. It's also why Suicide Squad got chopped up and brightened up. David Ayer has been very vocal that's not his movie and his was a totally different movie, without the pop song intros ext.
Here is what Steppenwolf looks like from BvS, which matches his look in JL trailer.
Snyder has always had awesome CGI in all his movies, it shouldn't be a surprise his CGI is so much better than the theatrical cut.
And even if by some chance this is all revisionist history, who gives a flying #### if it's better than what we got previously?