I've been a 1k out of SNA and ORD for over a decade and flown to all over from there on a regular basis. I'm not sure of data, but I can say for sure that the biggest reason it is hard to UG the ORD-SNA routes is the almost entirely 737 cabins on the route. Only 12 seats and from talking to flight attendants over the years, the vast majority are purchased F or GS on business days. The amount of times I have cleared CPU as a 1k on that route is very minimal. You better use an instrument. UA has also cut flights there and AA usually has at least 1 more route a day and their planes have 16 in F.
Good luck on this one, but I'm not sure UGs here are really any more difficult on UA these days than any other lengthy route. Try finding a flight over 3 hrs on UA that is not at 6am on Sat or 9pm on weds to use a RPU