I don't think it's a question of whether Warner has confidence in the product, I think it's a question of whether Warner has confidence in Snyder. But, more than anything, it just boils down to WB really needing this to be a megahit so they can finally get their own movie universe of the ground. It's pretty obvious they're trying to do in one film what Marvel did in fivefor better or worsein establishing and kickstarting that universe, so that means the stakes are very high for this film.
I mean, it literally says....
The Comic-Con trailer is impressively mounted and resoundingly loud, but what it doesnt appear to be is confident in its own product. By showcasing so much of the action close to a year before the full feature opens in cinemas, the promo does a disservice to fans by simply giving too much away.