The funny thing is he says at the end the problem is NOT with the laptop but with the connection. Just a small error in the video that not everyone picked up on. Yet as you said it is with how the TB3 is allocated once connected into the motherboard. The Core splits its connection between the GPU, the NIC, and the USB controller. It is actually splitting the speed between the IO on the Core itself... as well as what needs to be split in the motherboard of the Blade.