It was pretty unprecedented when Warner Brothers pulled Batman: Arkham Knight from the Steam store due to bad performance issues. The PC port really seems to have been in a bad way and Rocksteady are working hard on making it right.

It might not be right for a little while either. In an internal email obtained by Kotaku Australia, EB Games says:

As previously advised, we have stopped sales of Batman: Arkham Knight PC while Warner and Rocksteady work on addressing performance issues with the game. The latest information from Warner is that the updates won't be available until Spring. Due to this we have made the difficult decision to recall all PC stock from stores to return to the vendor until an acceptable solution is released.

Now bear in mind this means Spring in Australia which starts in September and could go through to November sometime. That is hardly ideal as I know PC players are desperate to play the game as it was intended. but you want Rocksteady to get it right this time. I say take the time you need.