I had an AWS c6g.2xlarge instance even set IOPS to 16k doesn't seem to help after one day. I've started a new AWS EC2 i3 instance with 900G ephemeral NVME SSD to verify whether an even higher IOPS can help sync eventually. Will update this thread if I got some progress. Date when the comment was posted: 2021-05-28.
Update 1
Some raw numbers to check during syncing:
i3.xlarge instance with ephemeral native NVME, IOPS 70K, iostat MB_wrtn/s was averaged to be about 10M/s
expand to see details
# /usr/local/bin/geth attach http://localhost:8545 --exec "eth.syncing"
{