Who is the best Batman?

[Aerys]

Soundwave said:

Aerys said:

 

Because it's meant to be a vision of an hypothetic apocalyptic futur with a world ruled by Superman, soldier of Darkseid, after the death of someone he loves ( and Superman becoming evil after the death of someone important is something we already saw few times  in comics or animated movie/serie), explaining the extreme measures batman takes in this dream vision which is not reality, the point of this sequence is only to make him even more determined in his mission and also to give him the information of what could cause Superman to change so much.( which is confirmed by Flash few seconds after)

So it fits perfectly the movie, the only question you could ask is how did he get this vision ? And this is where you can make theory like maybe the time travelling of Flash caused him this vision  of an alternate futur.

Time travel and dreaming are two different things. 

He didnt time travel himself, flash did, but he got a dream-vision of an alternate futur if something happens to the woman Superman loves.

So alternate futur =/= not the reality of the movie.