Coated canvas is generally quite easy care and durable, i actually prefer it to Saffiano but regardless both do work in less than perfect weather conditions. Most leather bags can withstand a fair bit, there will always be more delicate ones but the general kinds with good moisturizer care do fine. I have always carried leather bags and my weather is primarily wet(snow, rain, sleet etc)
You have to remember what else leather is used for to give an example.. tack for horses? you can keep leather halters forever they go out in rain, get chewed on.. broke etc. Saddle bags on motorcycles? what about the clothing ? again leather coats, chaps i could go on lol but point made.
