Having a WF/BvS film doesn't mean anything bad for Superman, because it's necessary.
For one thing, doing that movie before JL is way better (and my idea, btw) because if not, then Batman and the other heroes would've been showed horned in JL. Secondly, this movie represents what Snyder/Goyer talked about when it came to the sequel once MOS came out, one of them being that "the sequel and JL will be the cause and effect of one another". This and JL is that cause and effect. Third: this doesn't mean Superman's development is forgotten, because he was an outcast revealing himself to the world when his adopted home is threatened by his place of origin in MOS; going from that into JL would be a major gear shift for his character development because there are still things to address like "going global" like Synder said, Lex Luthor, the government, etc. The development Superman would to go through in This onto JL is knowing that there is a bigger universe, other people similar to him, and thus becoming a leader to them. And finally, while I would want more solo films, JL would have to be a franchise onto itself, right? Plus, this is what happened with the Iron Man trilogy and currently with Captain America. IM1 was just him (ignoring the SHIELD presence and Fury cameo), IM2 had Black Widow, SHIELD, and yes even people who wanted Stark to share his tech which became the development of him going onto Avengers, and then with IM3 it was his again with the exception of the Banner cameo. Cap feels the same way, with Cap1 just with him with Fury and SHIELD at the very end, and now with Cap2 we have Falcon, SHIELD once more, and Black Widow. MOS and its follow ups might be taking a page of that, but in turn, giving us more now than later, and the fact that this is a DC Film Universe, and they want to make sure all the other characters fit in and work together in that universe rather than being forced. Why not start with Batman with a sequel that may or may not a WF-B/S film?
P.S. I still want more solo films, but the sequel doesn't seem to be anything but a sequel at this time, and again, JL would have to be on its own, right?