I keep going back to the original post.

I'm not sure if this was a "what would you have done" vs "what should I do" or
just a vent

I have no beef with all the responses, just amazement at the thread interest so I'll just throw in my own

I would have done exactly what the OP did at the gate. Afterwards I would have formally objected to UA and expected a response, possibly with some mileage (never demand just suggest)