Yep, that seems to have worked. I moved a few large files over and they transferred. The data, single partition expanded to Data,single: Size:36.00GiB, Used:28.58GiB (79.39%) and after I deleted those files it shrank to Data,single: Size:28.00GiB, Used:21.02GiB (75.06%)
I'm not sure what any of this means tbh. One of the first things I did try was moving my VMs from /mnt/user/domains to mnt/disk2/domains to no avail.