Shout-out to @PotatoMania, my Arch on uConsole is a success! 
I set up my partitions using the guide for the RPi 4 here; then the pacstrap, the custom packages, the fstab, and the configs from the scripts here; and the user account manually using arch-chroot.
Coming from postmarketOS, I feel Arch loads faster. My Wi-Fi problem even went away, to my surprise.
I decided I don’t need gdm right away, so I didn’t enable the service. I can even simply disable NetworkManager, ModemManager, and bluetooth when I don’t need them. Assuming those, running just a vanilla console, I feel I can easily hit the exceptional battery life this device can promise.
My Bluetooth is missing as well. But I believe this matter has been fixed. And that my Git copy isn’t the latest. So I’ll just make it up as I go.
UPDATE: Bluetooth now works, as of 6.6.30.