Might be misunderstanding, but United is letting you change the route (X to Y) and dates between flights-- that's not the problem. What's messed up here is that United is not showing you the best prices available on the market when you're actually changing your flight, and that's regardless of what route or type of flight you're changing to.
To summarize, one of our users bought a flight and when they went to change it, United showed us the "new flight's price" as something almost twice the actual online rate if you search on United.com or GFlights.
Why do they have to be shady about it and just hide them without telling you why?
Maybe a little transparency would buy some goodwill and people would start giving United the benefit of the doubt.
Not all flights from X to Y are created equal. Some are direct, some connect. Some are at more convenient times. Some are on nicer aircraft. Some have more empty seats.
That seems... totally fair? Why should you be able to buy two flights from X to Y when you canceled only one? I get that prices are now lower, but your price is the same as when you originally bought the flight.