One of the issues with the RTL8153 NIC is (as a sibling commenter points out) that on M1 Macs, you are confined to the CDC-ECM driver. RTL8153 with this driver usually cap at ~700MBit and cause a lot of CPU load (usually restricted to the efficiency cores, but it's still pretty bad anyway).

For USB docks, I can still understand the choice. But IMO this is inexcusable for Thunderbolt docks. You can tunnel PCI-E, so nothing holds dock makers from hanging a good NIC with well-supported drivers on the PCI-E bus. Some higher-end Thunderbolt Docks do this AFAIK. The Apple Thunderbolt 2 Ethernet adapter uses a Broadcom NIC on the PCI-E bus and can reach 1000MBit without causing high CPU loads. Unfortunately, it requires a Thunderbolt 3 -> 2 adapter, which is more expensive than the Ethernet adapter itself.