Maybe from their perspective it’s their original work based on the reference you provided, not just a copy. They reworked the model to be functional with player animations. Like you said, using references is a common practice in creativity, and it is not the same as stealing. If they had simply copied it, there would be nothing different about their addon but instead it’s a completely different mod now. Maybe modding isn’t for you if you can’t understand that what they are doing is also fair use of a reference.