I just wanted to follow up on this. I ended up returning my XPS and got a Dell Precision with an Intel AX201 card in it. When I got the computer, I just moved the hard drive over from the old computer and booted it up. Download speeds were the same at about 2 mb/s. This computer came installed with Ubuntu though so I booted into there and checked which drivers were installed.
$ sudo dmesg | grep iwlwifi
...
[ 7.170627] iwlwifi 0000:00:14.3: loaded firmware version 48.4fa0041f.0 QuZ-a0-hr-b0-48.ucode op_mode iwlmvm
...
Booting back into Manjaro I found that newer versions of the iwlwifi driver were installed in /lib/firmware so I removed everything after QuZ-a0-hr-b0-48.ucode and rebooted. This seemed to have fixed the problem. I still have poor signal bars but am getting regular download speeds between 4 mb/s and 7 mb/s.
Why removing newer drivers fixed the problem? I have no idea, but it works.