yes the synthetic oils are not made from natural crude oil , they give better perfromance in terms of stability of viscosity , and are targeted at high drain intervals.
But still during making of synthetic oil 5w-40 will be a thinner oil than 5w-50.
5w-50 is targeted towards the high performance cars , sports cars, F1 cars etc .
so 5w-30 and 5w-40 will be good for daily driven cars like ours. Grande , corolla etc
In my experience i use 5w-40 in my 1300cc gli and it feels heavier in drive and i get milage of 13kmpl with stock tyres and alloys , than the people using 5w-30 in their car. its the difference in thickness which created the difference in viscosity grade.
The best brand of oil i have used in Pakistan is liqui moly but every body has their own preferences.
thicker oil like 50 at end may have their disadvantages if you are using them in a daily driven car , which is Engine will use more power because of thick oil and the milage of the car will decrease.
5w-50 is recommended for Sports car and Track cars. there is absolutely no need for using it in a family car like Corolla. I have made a mistake once by using in gli .
Some references from where i read :
Oil types, ratings, viscosity, choosing good oil
Oil Specifications Explained - What does 10w40 mean?
Synthetic vs Regular Motor Oil: A Sun Valley Automotive Terry's Tip
Oil Labelling Explained - TechWiki
(NOT THAT I AM IMPLYING I AM RIGHT BUT SHARING WHAT I UNDERSTAND AND UP FOR LEARNING MORE)