Non-official usb-c dock station detects 2 external monitors are a single one
The setup you with that hardware is not going to work - and cannot be made to work.

The USB-C dock station you've got works as a MST (Multi-Stream Transport) hub. MST is a part of the DisplayPort 1.2 standard, which makes it possible for monitors and computers to support "daisy-chaining".

Daisy-chaining is most often seen where the monitor has both an input and output DisplayPort adapter, allowing you to connect the first monitor to the computer, and the second monitor to the first monitor. If both monitor and computer support MST daisy-chaining the two displays will act as seperate displays, exactly like if they had been plugged in directly to the computer. 

In this case MST daisy-chaining is used within the dock to allow dual monitor outputs. Note that because the monitors share bandwidth, it is not possible to connect them at the same resolutions and refresh rates as possible when using seperate cables connected to the computer. With your monitors it shouldn't be a problem though (they're relatively low res).

The problem for you is that macOS does not support MST daisy-chaining. This is a software limitation and not a hardware limitation. Instead macOS supports daisy-chaining Thunderbolt monitors (such as with the Apple Thunderbolt Monitor).

You've got it working on your ArchLinux laptop because Linux supports MST. In fact you should be able to run Linux on your MacBook Pro and drive both displays via MST that way.

To get a setup like this working with  macOS, you'll need a Thunderbolt 3 dock instead of a USB-C dock. Or you could individually connect the displays to the MacBook Pro. For example one display connected to the dock, and the other connected via a USB-C to DisplayPort cable.