Synthetic leather is literally "knock-off" leather, never is synthetic preferred to the real thing unless you are cost oriented, or vegan. Synthetic boots also tend to be made out of lots of pieces of synthetic leather, stitched together with other types of materials in the uppers in fancy patterns, which leaves them vulnerable to being penetrated by water.
I hike in full leather boots, I currently have a pair of Mammut Brecon boots as my backpacking in the woods boots.
And a pair of Zamberlans for off-trail hiking, scrambling, climbing and wearing crampons.
A long time ago, a seasoned hunter and bushman who has been through more pairs of hiking boots than I will ever own in my lifetime offered me a valuable piece of advice in regards to hiking boots:
"If a needle has gone through it, then water can get through it."
You'll notice that the boots in the images above are made from one piece of leather. Not only is leather still one of the most durable materials on the market, but having a boot with no seams means there's nowhere for the water to seep in.
I know that a lot of companies boast having synthetic waterproof boots, but they're only waterproof for as long as their waterproof coating lasts. As soon as you get some wear on them, in my experience, the waterproofness begins to diminish.
The only disadvantage to such boots, is that they are not the boot of choice for super hot weather, they don't breathe exceptionally well so your feet tend to sweat when it gets hot out. You need to pack extra socks and change them more often to regulate moisture inside your boot (I wear marino wool socks year-round, they are literally the only socks I buy).
But the pros far outweigh the cons, leather boots are stiffer, more stable, more durable, more waterproof, and last a lot longer. You'll probably spend as much or more money wearing through multiple pairs of synthetic boots in the amount of time it'd take you to wear out one pair of descent leather boots.