I agree that they should had just used Diana as a person he was battling with and then she just started pressing him about what he saw in her and why he liked her.
They still could have had The Gentleman's deception as part of the story. Then Selina comes in and saves the day, blah, blah.
I mean, maybe there could had been a scene or panel where Selina walks with Bat to meet Diana and then she just has this "look" on her face like, "wow, Wonder Woman" and then at the end, he could had reassured Selina that she is the only woman he wants.
The End. LOL!