So I notice that cheap $20 USB-c hubs (no power supply) lower transfer speed for connected devices. This isn't surprising, after all my laptop only have 1 lane and now all the mouse, keyboards, external SSDs are sharing it.
I recently bought an expensive $300 Belkin TB3 Dock Pro, it is independently powered by it's own power brick, and everything is fast, almost as fast as it would be without a dock. So I wonder, what is the technology behind this?