I am not a petroleum expert either, but I have done a lot of reading on the topic of engine lubrication. It seems undisputed that synthetic oil retains its viscosity much better than conventional oil in cold temperatures. It therefore reaches internal parts of the engine more quickly and prevents metal to metal contact that causes wear.
Synthetic oil would also prevent shearing under very hot operating conditions. Shearing is when the oil film protection breaks down and allows metal to metal contact.
My personal experience supports this. I keep my cars (GMs) for a long time and average well over 300 000 kms before I trade. I have never experienced engine wear symptoms with those cars. For instance, even at those high mileage levels, I never have had to add oil between oil changes. And the engines always retained their power and fuel efficiency.
The other advantage of synthetic oil is that they are not petroleum based, which makes them greener.
From what I have learned, conventional oils of today certainly offer adequate protection. Most people use them, and cars today outlast those of yesterday by a wide margin. I remember when an engine had reaches 100 000 miles, it was at its limit, and “ring jobs” where required.
But I still use synthetic oil because I simply like to have the impression (justified or not) that when I start the engine at 20 below, or drive for hours in hot temperatures, minimal damage occurs to the engine.
BTW, a person earlier reported that the temperature gauge rises more quickly when the car is not driven. I have not observed that, but if its true, it could be explained this way: the temperature gauge measures the temperature of the coolant, not of the internal parts of the engine. When a car moves the heat from the coolant is dispersed, giving the impression that the engine itself is colder.