are you suggesting that if one uses GM Dexos1 there's a good chance they will run into timing chain problems around the 40-60k mile mark?
Yes. Here is a Google search to show how prevalent it is:
Nissan Timing Chain Tensioning System Problems
We have been studying these in depth since 2008 when GM introduced the LLT version of the 3.6L engine, and it is not the design of the chains as we see wear to the tensioners as well as the chains themselves, and almost all premature failures the owner had used the deal/owners manual oil recommendation. In the few that the owner drained the factory fill by 500 miles or so and only used a full synthetic, we have seen no significant wear issues, so we have attributed this to the raw fuel dilution of the oil and the high abrasive particulate content.
Think about these engines compared to the LS family of V8's that were only to run M1 full synthetic. These rev higher, have far more critical moving pasts, and far more of them dependent on oiling and proper oil pressure being maintained, yet the V6, considered an "economy" choice is recommended to use the cheap syn blend. Compared to a full syn at the same miles of use, viscosity in both ranges measured is far less when run in a GDI engine than a full syn at the same interval. The syn oil leaves no sludge. That is caused by the higher heat ranges these engines run internally that breaks down the conventional portion of the blend. Now, the DEXOS rating standard by GM is even stricter than API, but these engines, after initial ring seating, (and this is the best method:
drain that factory fill full of assembly debris and filings from break-in and ONLY run a full synthetic. We also see the internal parts have no or little discoloration on them from deposits unlike the blend leaves.
The reason the small engines are recommended to use cheaper oil, and lower octane fuel (even though at 11.5:1 compression ratio 93 makes a good improvement) is purely for marketing to appeal to the budget minded owner, or potential buyer. If the same slot vehicle offered by the competition if GM stated to use 91/93 octane and full syn, that would be jumped all over like Ford using lightweight aluminum in the truck beds VS heavier and cheaper steel.
Rarely is what is best for a engine/vehicle is inline with what is the most effective for marketing to a certain demographic.
Having spent time in research facilities with dyno cells full of engines run to certain hours and then tore down and inspected, it is easy to see the advantages of using a full syn (and yes, M1 is a great oil, but there are better IMHO) vs a dealer pushed blend. These are things the consumer generally never thinks of though. Having these forums gives those looking to learn and gain knowledge a place to do so, but there will always be detractors that wish to mislead or confuse for whatever reason they may have.