What you say is correct except unless the oil was overheated such as blowing a radiator hose or such. Getting oil hot will crack down the molecules and change it’s properties.
You’re right. Too much heat puts a fork in it.
Synthetic oils will not break down like conventional oils under engine related heat.
The molecules are made to be stable which is why it is called synthesized in the first place.
The only thing that will lubricate in space is synthetic oil. Also, Helicopter/Turbine bearings reach 500 to 700 degrees in the Hot-End and the ONLY thing that will lubricate them is Synthetic.