Its tough to say what a good oil is.
Do you run a certain oil for hundreds of hours and take the engine apart, measure everything which is a wear item and do it again with another new engine and a different oil?
Has anyone experienced an engine failure due to poor oil?
My perspective is following:
A full synthetic oil is the best. It is made from natural gas, atoms are put together into molecules that do not allow easy oxidation. Oxygen atoms have a tough time connecting to the oil molecule chains. Oxidation damages the oil, that usually happens at elevated temperatures.
There should be a decent amount of ZDDP in the oil to mitigate wear but still protect the emissions systems
Detergent cleans the engine, most oils have a decent amount. Same with dispersants keeping contaminants from settling and making sludge.
Regarding Viscosity, I prefer a light oil XW30 or even XW20 due to improved fuel economy, lower friction, more HP, better cooling. When the engine is hot, it just flows more oil through the bearings cooling them down.
A light oil when cold 5WXX or even better 0WXX flows better to the bearings. It protects them from running "dry" at startup or shortly after.
Oils which have a big spread in the viscosity numbers like 5W50 have a lot of VI improvers. These break down and after some time you end up with an oil that is similar to a 10W30 as an example.
My perfect viscosity would be a 5W30 for the Cummins. Low VI improvers and light for good flow.