I don't think they are purposefully making this Superman a "moron". I feel people tend to forget this particular Superman has only been on the job for what? Two or three years? He's still young/inexperienced and most likely still doesn't fully understand his powers. While old man BatGod has been at this for a long time.
It's not unusual for superman, especially younger superman, to not give a fuck about practicality and rely heavily on his invulnerability. He doesn't dodge bullets and usually just tanks everything. He's been called out on this by Batman in the past because yeah, it's pretty lazy and arrogant of him.
Superman does not take him seriously. It's mistake that almost everyone more powerful than him makes.
Lots of good food for thought. In this version you would think Superman would be at least a little wary - given the reputation a well established Batman would have. I must admit the anticipation of the fight is a bit of a double edged sword for me - something I really want to see yet dread will be handled in a way I find implausible (in a movie about super heroes).