Manufacturers have been trying to shave grams off of the runner weight for decades, just like they've been trying to do to all the equipment. They switched the holders from metal to plastic. Then they added holes to them. Then they added holes to the steel runners. T Blades made a runner that was a smaller piece of metal and a lrger plastic holder. Bauer tried fusing aluminum to the steel. Now they're trying that with carbon fiber.
If there was no tangible benefit, skate manufacturers wouldn't have been trying to cut weight essentially since they started making skates. I agree that the redution of even 35% of the weight of a runner, which results in just a few grams, is likely not going to make anyone faster or better when taken as a weight savings. However, there are two reasons I can think of that would actually make a difference and cause an improvement in performance.
The first is overall weight distribution and balance. These runners are being included on Bauer's flagship skates. Those skates are incredibly light overall. Changing the distribution of the weight by even a few grams could make a pretty big difference to how the skates feel to the player. Reducing the amount of weight underneath the foot would likely improve the feeling the skater has with the ice. CCM has gone to one piece boots, not just to cut overall weight, but to eliminate the midsole and the weight under the foot as a result. As an example of this, forget the weight of composite vs wood sticks where the difference is huge, but look at how changing just a few grams here or there can result in a composite stick that feels too blade heavy, or not blade heavy enough to give good puck feel. Look at how adding one or two grams of lead tape to a golf clubs changes the swing weight and performance.
Second is playing off T Blades design, and goes along with the development of countless methods of reducing drag like blade profiles, FBV, Z Channel, Flare blades, and many others. Skating creates friction between the metal blade and the ice. That friction heats the metal and causes surface melting, that melting is what allows us to glide on the ice. When skates are too sharp, the edges penetrate the surface melt and dig, reducing glide. By reducing the amount of metal in the runner, you also reduce the mass of the blade. Reducing the mass of the blade allows it to heat faster and higher, causing more surface melt, and increasing glide. An increase in glide and a reduction of drag could increase overall speed, manueverability, efficiency, and endurance, far more than the simple reduction in weight of a few grams could. Plus, less metal likely means less rigidity, and more flex on the blade. That flex creates more energy return, acceleration, and stopping efficiency (part of the theory behind Bladetech runners).