Yeah there wasn't a good reason to make Einhorn trans. I don't think they intended it as a broad commentary on trans people generally and that it was just supposed to be "this guy was so messed up after that botched kick that this is how far he went to get revenge." But it doesn't really matter what they intended if the result was just having their villain be an unhinged trans woman.

That's not even to say you can't have the villain be a trans woman either. They could easily just have had the broken Ray Finkle get therapy, realize that he was actually she and rebuild her life, then finally as she's got her life back and she was finally happy again who happens to show up and ruin everything yet again? Dan fucking Marino. Basically the entire fucking movie could have happened the same way. She could even still have killed Podacter for finding out about "her past" as they more crudely put it, but you'd probably want to make it where he was going to blackmail her or something. Idk.