The engines did have lower overall hours, yes, but the suggestion they need whole overhaul after very few hours is because it looks so when looking at it from USAF doctrine where "removing engine and sending it to special facility" is only for rare complete overhauls, and local mechanics are supposed to do regular minor work all the time.
MiG-29 instead was done under doctrine that the airbase does not have mechanics capable of doing such overhaul, nor the facilities to do so, and instead you swap the engine and send the used one to maintenance facilities further away from the front, same with other aggregates.