Interesting theory, and I'm no expert, but it doesn't feel correct to me. Of course United flies only jets, but it has a variety of regional partner airlines that also fly only regional jets.
In a slightly similar way, FedEx operates only jets but for small cargo routes seems to operate only propeller planes (along with its large FedEx feeder partner feelts)[1]. This could be for a variety of reasons, but it seems most logical (to me) to assume that props are more economical and of course cargo doesn't care about comfort.
In a slightly similar way, FedEx operates only jets but for small cargo routes seems to operate only propeller planes (along with its large FedEx feeder partner feelts)[1]. This could be for a variety of reasons, but it seems most logical (to me) to assume that props are more economical and of course cargo doesn't care about comfort.
[1] https://en.wikipedia.org/wiki/FedEx_Express#Fleet