How the motors run are part of it, but hours are hours and some things on the engine only last so many hours.....raw water pumps, starters, alternators, exhaust manifolds, etc...….some things go by cycles...…..most manufacturers state engines do best running at 80% load...…. and generators do tend to easily run twice as many hours as the same main engine in a yacht. a 3412 generator or pump that runs constant rpms (and loaded properly) for days and days on end will go many more hours than a yacht engine that runs variable rpms. Other manufacturers state fuel consumed......cat does both.... I wouldn't say 3412's with 5300 hours and run easy is the same as if the engines had 1500 hours and run like a typical yacht, maybe equivalent to 4000 hours run normally. My guess, but who knows...….. I've seen well maintained engines grenade out of the blue for various reasons with much lower hours.....drop a valve or seat, split an injector tip, aftercooler leaking on a 2 year old engine. etc.