In my experience, the textiles (Cordura) are not all they're cracked up to be when it comes to ventilation. You can't beat a waterproof textile in the rain, however.
Leather, most certainly, will provide little to no ventilation.
I ride with a Kush!tani mesh jacket in the summer, and yes I sacrifice some safety for comfort. I have a Dainese leather jacket I wear when it's not hot and humid. I also have a Cordura that I rarely wear.
Joe Rocket offers their Phoenix jacket and it's incredibly popular, but it's not Cordura. I suppose it's just a question of how much safety you're willing to sacrifice.