Yes, the RR on the 757 is hard to beat. Is there a more reliable or lower operating cost engine anywhere?
That said, why are so many 757s being parked, and maybe scrapped?
Airlines can be more rational than militaries when it comes to loyalty. America West 757s came with RR because Indian Airlines had ordered them before going bankrupt.
Boeing and GE financed Continental's bailout from its second bankruptcy in the mid-1990s, with the agreement that CO would always buy Boeings with GE engines. RR was selected for CO 757s by GE, because they were the weaker competitor.
IF the militaries had any common sense, they would buy half-life airliners, including 757s, for tankers. They would save hugely, as the work could be done competitively by MROs all over the world. However, govt leaders everywhere are rewarded for spending money, not saving it.
GB