This claim, which goes back decades with little/no evidence, does more harm than good.I'll stick with what the manual says. For those that do their own oil changes and use something not to spec, don't expect warranty protection if something happens.
- Recommended oil grades/weights are a compromise of competing needs, directed at the average driver
- We have millions of engines' worth of data on the merits of going a grade heavier to protect under high load/temp conditions
- Many automakers even recommend heavier grades when tracking the car or otherwise operating at high temps
And if you click my prior link, you'll see that A5 is not (or was not) the spec, it was A3. A5 trades away the high temp/high shear additives in performance-oriented A3 for slightly better efficiency. But it's mostly moot as actual examples of warranty denials outside of clear abuse are basically nonexistent.