I use NFS to mount a directory in my Debian VM and I tried the new virtiofs. It was around the same. Is that expected?
virtiofs
sudo sync; sudo dd if=/dev/zero of=/mnt/test/output conv=fdatasync bs=1G count=5
5+0 records in
5+0 records out
5368709120 bytes (5.4 GB, 5.0 GiB) copied, 6.29989 s...