Hotter is ok because hotter we are talking maybe 5 degrees, not even a blip between a 40 and 50.Increasing oil weight for hotter climate will only make your engine to run hotter with no increase in longevity...
Increasing oil weight within manufacturers recommended 10/40 to 20/50 WILL vastly improve shift quality in shared sump bikes for those that ride in warmer 90 to 110 degree weather vs those that ride in 70 to 85 degree weather.
One size does not fit all for the manufacturers giving you a choice, common sense and repeatable results over and over.
Many motorcycle manufacturers give a choice between 40 and 50, common sense dictates the climate you ride in.