Per my experiments, only a small part of I/O time goes to actual reads (and writes) of the content. The rest is (assuming that SNO follows the most basic setup) database and file metadata updates. What’s more, some SMR drives seem to be performing additional maintenance writes even when drive is only read from, some kind of imprompu defragmentation, which make the operation even slower.
The extra effort I wrote about is things like moving databases to different storage, which moves some I/O to different units, or adding caches that help the drive defer some writes in hope to reduce write fragmentation.