For frictional minimization, yes the thinnest oil that prevents excessive friction across the expected temp range is the correct recommendation.
The antillary is not true, though. It is not accurate to say that any thicker viscosity is ok because it provides a thicker lube film, because thicker viscosity will also slow oil flow rate for the fixed oil supply plumbing, and we don't know at what higher viscosity this will starve critical parts and not remove enough heat. That's why I stick with engine builder's latest viscosity recommendations. Becomes even more important when engine oil is also used as a hydraulic oil, where flow rate is critical to solenoid valve operation and timing (VVT cam phasers, MDS valve lifters, etc.).