It is a real shame they use the Killer (Atheros) WiFi. The developer edition used to have an Intel WiFi - have they changed that?
That said, I haven't seen any issues with Killer WiFi (XPS 15 9570 with Ubuntu 18.04.01), but I do have an Intel WiFi card if the Killer needs to be replaced.
Also I do use a USB3 to Ethernet adapter at work (I have always prefered a wired connection for work when available).
The Killer WiFi issues to me seem to have been related to the Windows driver. Never had any issues on Arch, and an update last year (not suggested by the Dell update tool, check the website) fixed it for Windows.
That said, I haven't seen any issues with Killer WiFi (XPS 15 9570 with Ubuntu 18.04.01), but I do have an Intel WiFi card if the Killer needs to be replaced.
Also I do use a USB3 to Ethernet adapter at work (I have always prefered a wired connection for work when available).