Maybe someone needs to do some more research, or buy a better synthetic boot. Leather absorbs water....fact. You can condition them, same as you can synthetic, but it only last a short period of time. Plus, once leather gets wet it becomes much heavier than synthetic material. Let's not forget its the "booty" inside the boot that keeps your feet dry not the outerwear of the boot. Now if we were talking durability, I may side with you.
I have never had a synthetic/gtx boot stay waterproof for more than a year. My 5 year old leather/gtx zamberlans can still handle full submersion in a creek without my feet getting wet. Yes I treat them, yes they can get wetted out (in a torrential texas downpour, hunting in waist high grass all day), but they damn sure are still waterproof enough for me after 5 years. And the idea that they are heavier when wet than synthetic is kind of a joke... the only added weight to either boot is water weight. Leather isn't inherently heavier than synthetic.