I have the XPS13 9380 (also 2018), and it came with an Atheros WiFi chipset (Killer, I believe). Looks like the Bluetooth is on separate hardware here; lsusb reports it as a "Foxconn / Hon Hai" chipset.

I don't really use BT for anything, so I can't comment on its quality. WiFi has been completely fine, though. Either way, I believe both the WiFi and BT hardware are soldered in on this model.