New sprocket - Alloy or cromo?

31trum: rear sprocket will turn ~3 times for every turn of the front (assuming something similar to a 48 front, 16 rear), so you would expect it to wear out 3 times quicker.

Funny, i always thought that the sprocket will wear out quicker because at all times less teeth are in contact with the chain compared to the chainring. Thus the forces working on the sprockets teeth are bigger than in the front.
Somebody please correct me if i`m wrong.