I've had similar experiences with highend carbon fibre sporting equipment and in my experience it really depends on the brand, design and manufacturing process as to whether the equipment is super light but fragile or a little heavier and more durable, as Piros said some manufacturers are now using a combination of materials to produce boards that are relatively light but much more durable than they once were.
Rob Stehlik from Blue Planet explains it quite well in this little vid from his YouTube channel. I've been riding his boards now for while, and while they're not the lightest boards in the industry they are certainly more durable than others I have ridden.