DisplayLink is still DisplayLink running what is an basically external graphics card over USB (vs an internal one on PCIe).

However DisplayPort over USB-C/Thunderbolt 3 can use the internal graphics device and therefore isn't subject to bandwidth limitations of USB-C/Thunderbolt. That said 5/10/20 (USB-C) or 40 (Thunderbolt 3) Gbps should be plenty to run half decent graphics. Even USB 2.0 did a reasonable job for general coding/office type duties.

The bit I'm confused over is whether the USB-C/TB3 to DisplayPort adapter I have actually runs USB-C or Thunderbolt 3. I think it's only USB-C. Thunderbolt 3 allows 2 x 4k@60Hz displays.