I only have 1 jacket, a vented leather Teknic with removable quilted liner.
I wear it with and without additional liners for anything in the 32-90 degree range and it’s comfortable.
No argument that it can get toasty on hot days, but I’m rarely in stop-and-go and a bit of movement helps alot. One benefit to stiff leather (at least on my jacket) is that the venting tends to stay wide open and it can flow a lot of cooling air.
Worse than heat to me is when the temp comes with high humidity. Then the leather can feel clammy and uncomfortable.
As for rain, I’ve been caught in it and the jacket has dried to original condition (you have to be very careful how you hang wet leather). But I generally avoid riding in the rain and would definately agree with earlier comments about textile’s advantage in the wet.