Where I live, it doesn’t rain all that much, and cools down over night. But regardless, my preference for a leather jacket is its social versatility – when I use my bike as a primary mean of transportation (late spring to mid fall), I just don’t want to look like a dork when I arrive where I wanted to get. You can always wear a leather jacket and look ok, while, once the MC is out of picture, armored textile jacket on a person just looks and feels … I don’t know.
That especially goes for overnight trips, like night or two. Definitely don’t want to carry two jackets because I might need one when I get there where I will be spending a night.
And my experience with the rain is, if it sprinkles anything will do, if it pours, especially at speed, nothing short of dedicated rain gear will work right