From the passenger's letter, it's obvious he believes he was mis-treated.
But I think he still got treated well. The deal he got (Y to C) is more than fair compensation for a 2-hour delay. I'm sure UA would find more than enough people willing to do this for a C upgrade.
He claims the TA offered a first class upgrade to a Y passenger (and a 2P at that) for a voluntary reroute. It might be true but I think there was some confusion here somewhere. The agent probably screwed up and did something without authorization. If this is what happened, the agent should be given corrective/remedial action.
But reading between the lines, it sounds to me that the passenger is an issue as well.
Probably started at check-in, where a 2P member flying on a cheap coach fare makes outlandish, arrogant demands:
I would not have not have agreed to give up my seat and change my international travel plans for only a Business Class upgrade, but I thought it would be worth it for the offered First Class ticket.
The chit probably hit the fan in the F lounge. And the arrogance continues and escalates in the letter. I can only imagine that his interaction with the staff in the F lounge was of similar tone and caliber. If that were the case, and I were that staff, then I would certainly do my best to play things by the rules and to reverse this double upgrade.
I was lied to and cheated by your employees.
My flight was over-sold, although I had a confirmed seat on the aircraft.
(I) would have to settle with (sic) Business Class.
At this point, I had extreme feelings of being frustrated, taken advantage of, and cheated. I feel as if I was swindled and given the old bait-and-switch routine.
your employees can not be trusted and make promises they cannot keep,
(I) will start looking to fly other airlines which will treat me with respect as a valued customer and frequent flier.
I will look to book all my future, scheduled international and domestic travel for myself and my business associates on American or Delta airlines.
If it were me receiving a letter like this, I'd say "good riddance."
Your friend may have a valid claim, but should do a reality check first. He got an excellent deal. Maybe not the one someone (probably) offered improperly. But an excellent deal nonetheless.
If he's unhappy at this gift and wants a bigger one, suggest he rewrites the letter from scratch. Keep it simple, and take the vitriol and emotion out of it.
a) deal negotated was (x) with the helpful agent.
b) understand that (x) is not according to policy; should have received (y). But if offered (y), would not have taken the package.
c) feel you are still entitled to (x), which was the deal. Not your fault agent went beyond her authority; she still represents United.
d) suggest a resolution.