I don't agree with the thoughts that the OP's friend got adequate compensation. Our judgement on that is not relevant after the deal's been struck. This case is clear. There's no "he said, she said" involved. He had a BP. I think this comment is very applicable:
(should) focus on the humiliation the passenger faced, and how he was treated (were they nice about it or treat him like dirt or a criminal, etc). Also, it's about UA's employees having the authority to make a decision and how would you as a passenger know they have that authority after this experience so how could you ever trust what you're told after this experience of essentially being told by the rep B that rep A is clueless and wasn't allowed to do what they did.
I agree with the recommendation to recast the letter in this light. And specifically ask for two SWUs.