There are many variables
Frankly in no other mechanical/transport endeavor do owners have more choice. Requirements of Aviation vary wildly depending on mission profile, acquisition cost, maintenance, training and useful life. Keep in mind the ultimate owners and manufacturers are locked in design from blank page. This is not a trip to the showroom and a hurried decision between DOHC-6 and QohcV-8. By the time metal is poured and designs are set, the powerplant is an inextricably dependent part of the airframe. Still, some options re: manufacturer can be exercised. The RRTrent @ 95k thrust, is every bit the equal of the GE90. Packaged decisions by this time have little if anything to do with power, economy, spares etc. The complete airframe with powerplant is a design from scratch endeavour. When power leads aerodynamics (leRhone, Liberty) frames are designed around powerplant. When aero leads power, (F-16) the opposite can be done. They are no less completely inter-dependent.