the major engine OEMs aren't investing enormous amounts in optimising for a startup airframe program though, so at best you're getting a derivative of the engine on the equivalent sized Boeing/Airbus program with roughly the same fuel efficiency but worse expectations in every other relevant area (expected reliability, competitive local maintenance markets, type-rated crew availability, commonality with existing fleet, residual values etc, and probably worse aerodynamics and structural weight) due to the airframe program's relative immaturity