Looks like they closed the flight at 9:00 PM (image here), 5 mins. early.

Clearly the GA or ops (or whomever) thought you'd misconnect. But I don't think it's unreasonable to expect that they'd at least hold the flight until, oh I don't know, the actual departure time. Obviously it would be ideal customer service to hold a flight a few mins. for any customer, but this really was a poor decision on someone's part. (And FYI, I have been on CO flights that have been held upwards of 30 min. so that a customer would not misconnect.)

IMO, you were IDB'd and you should be compensated as such. If they closed the flight at 9:05 and you hadn't made it by then, I'd feel differently (even if I think they should have seen your inbound flight's arrival time and used some common sense to hold the flight for an extra 5 mins. or so).