Hi,
On macOS you can copy files that are open for write, "no problem".
Easy enough to test, open a VM, run it and hit duplicate in Finder while highlighting the bundle.
It will copy the VM, all files are getting duplicated. But as the files are open for write there are no guarantees you can use that copy.
In that case you are copying files locally, so it is fast.
With TM backups the files are copied over a network link, so the disk will change over time and chances the backup is actually usable is much lower.
If a VM is suspended, no files are open by VMware Fusion and you can copy it, as long as you use it again on the same hardware and as long as there haven't been CPU/GPU errata updates.
As mentioned in the article, from what I understand the TM algorithm is age and file size.
So when it needs more space it will first delete larger files that are a bit older.
I might be wrong though, but this is a problem that has existed since VMware Fusion 1, VMware has looked into it before and AFAIK it is not fixable on their end.
FWIW, I use TM myself and like it a lot.
But I do not trust it with my virtual machine backups.
--
Wil