When you look at the properties of both that is for 5W20 and 5W30, there is a big difference in viscosity @100 degree centigrade as per specified test method (ASTM) as below:
For 5W20 it is 8.9 cST (always below 10 cST)
For 5w30 it is around 11 cST (always above 10 cST)
With tropical and hot areas (like Pakistan) it is rule of thumb to ensure that the viscosity remains above 10 cST at 100 degree centigrade to ensure that the oil film ensures its presence between moving parts preventing wear and tear and provide cooling.
With viscosity dropping to 9 or 8.9 at 100 degrees and engine operating at 40 degrees of ambient temperature, the film can break and its presence between the moving parts is compromised eventually leading to wear and tear.
If a vehicle is imported to some other country other than for which it was manufactured and oil viscosity recommended by manufacturer, the recommended viscosity has to be re-evaluated as the new country shall have different weather conditions.