Except they understand the lead character so you cant say it's shoddy, to bash this version of Batman is not understanding the character, not knowing all it's iterations.

You clearly didnt read a lot of comics , it's simply not true. It seems like a lot of people you didnt understand all the movie and believe what happens in his dream is the reality. But it's not, it's just a dream.

And like i said, it's a lie to say Batman is a mass murderer in this movie compared to other batman movies, he kills less people than Bale in Nolan's movies, and even less than previous batmans.

What the hell was even the point of this dream sequence? What plot point does this advance? 

Why not have a Batman dream sequence where he rapes the Joker with a giant dildo while we're at the whole "lets have a dream sequence where Batman does things he normally would never do" type thing. 

Yes I would say not understanding one of your lead characters is "shoddy" scriptwriting. Honestly it gets a lot wrong about Superman too. 

This isn't the first "dark" version of Batman, lol, Hollywood has been doing dark Batman since 1989 and profiting handsomely off it. 

This is the first psychotic mass murdering, gun totting Batman though. I don't see that as neccessarily true to the character at all though. 

In this movie if Clark's mother was named anything but Martha, he wouldn't been blugdeoned to death with a freaking dirty bathroom sink by Batman, lol. Even in the Dark Knight Returns comic, Batman is never that much of a murdering nut job (he fights Superman but uses a low does of Kyrptonite to teach Superman a lesson to stay out of his way, but never intends to murder him). 

If this is the "best" Batman, then IMO a lot of people don't understand this character at all. 

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.