Allowing the rings to settle into the piston's groves isn't the same as a break-in. A break-in period was used to wear down the high spots on bearing races and cylinder walls. It used to be that the machining done to build a new engine wasn't of very high quality and the parts needed time to wear into it's mating surface.
Do these 'experts' build engines or just write articles in magazines?
I can't speak about any problems GM may have had with the Corvette as I don't know anything about any problems they may have had. But the truth is that, under normal conditions, there is no difference between synthetic oil and conventional oil when comparing their lubrication characteristics. There is a BIG difference between them under abnormal conditions of temperature and high stress (extended full throttle, full load).
Unlike you, I have never used Mobil 1 or any other synthetic oil in any of my cars. I do not trade cars until the cost of operation becomes too high. I really don't care if I'm driving the latest and greatest or not, I just want dependable transportation that doesn't cost too much. That said, I keep all of my cars for at least 10 years and most of them have run over 100,000 miles of mainly city/town driving with few high speed extended trips.
With one exception, the condition of the engine is never the reason why I trade cars. Most of them started needing too much maintenance to either the body or the running gear. I can't see spending $2500.00 to rebuild a transmission in a car that is only worth $3000.00. The one exception was a 1982 Dodge with a 2.5 L engine that broke it's cam and beat the head to bits.
I'm glad you are getting good service out of your cars. But don't think it's because you use synthetic oil. You would get the same service out of your cars if you used name brand conventional oils.
Jack