If you do OLCI, you are still subject to a 45 minute cutoff for checked bags. And you still need to stand in line to check your bags. I guess if the airport has an OLCI bag drop, it's a bit easier, but there still may be a line. As far as using a kiosk, often you access the kiosk through a line. The free standing kiosks often don't accommodate checked bags.

The best way for a customer not to have this experience is not to check bags, but obviously for some trips that's unrealistic. The best thing UA could do to avoid this situation is to sweep the line when a flight is approaching the baggage checkin cutoff time. That way people who are going to miss the cutoff due to a long line get accommodated. Some stations do this at certain times, but it's definitely the exception.