I am playing it on a 3080 at 4k. It's a good looking game and mostly runs fine. Some outdoor areas and the bike get iffy at times and you can drop into the 30/40s. The poor GPU / CPU utilization does sound like that from a technical perspective these guys had serious issues.
Also unreal 4 is a terrible open world engine per DF. I wonder if they also consulted with Rocksteady, they are also using unreal engine for their open world looking suicide squad. Pretty sure this happened before also with Arkham Knight with the batmobile sections (unreal 3?).
At any rate doesn't hurt my enjoyment. Can't blame the people complaining, we shouldn't forgive/encourage sloppy programming jobs. The rest of the game is quite good though and quite fun, if it wasn't for the performance it would have likely pushed closed to 8/10.