Worse, they also determined that there is a resonance issue that can cause an engine to fail prematurely when operated for an extended period at max con power
The opposite is true. The resonance occurs at LESS than Max Continuous power. If you read the Boeing Bulletin you’ll see that in the event of an Engine Failure crew must operate the aircraft during the subsequent diversion and do it at as high a FL as possible to keep the remaining engine out of the resonance ‘range’ and close to MAX CON.