Well I looked at some more things but then the usb 2.0 / esata enclosure seems to be faulty and is not working in Devuan too with 500GB drives at least, it still works with smaller ones although the online specs say it supports any size and it used to. I tried both 500GB drives in that and they won't mount and give a partition size in TB with fdisk -l. So it seems the answer is simply faulty hardware and unhelpful coincidence creating patterns that seem to have meaning but in fact are randomly generated.
Dell M4500 lsmod in Artix:
diff between no drive plugged in and then USB 3.0 drive plugged in but not mounted:
+uas 32768 0
+usb_storage 86016 1 uas
no change when swapped from USB 2.0 port to express card 3.0 adapter.
diff after drive is mounted, placed back in 2.0 port:
-uas 32768 0
+uas 32768 1
-btrfs 1998848 2
+btrfs 1998848 3
-crc32c_intel 24576 3
+crc32c_intel 24576 4
no change when unmounted, swapped from USB 2.0 port to express card 3.0 adapter and remounted.
Installed power packages:
acpid 2.0.34-1
cpupower 6.0-2 (linux-tools)
mate-power-manager 1.26.0-1 (mate-extra)
upower 1.90.0-1
Some testing in Devuan, same result in Artix now:
$ sudo mount /dev/sdc1 /zmnt
mount: /zmnt: wrong fs type, bad option, bad superblock on /dev/sdc1, missing codepage or helper program, or other error.
$ sudo fdisk -l /dev/sdc
Disk /dev/sdc: 465.8 GiB, 500107862016 bytes, 122096646 sectors
Disk model: 00LPLX-08ZNTT0
Units: sectors of 1 * 4096 = 4096 bytes
Sector size (logical/physical): 4096 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0xa9d2e011
Device Boot Start End Sectors Size Id Type
/dev/sdc1 49152 972578815 972529664 3.6T 83 Linux