If all you’re doing is an smb share i don’t see how a windows box is any more effort to maintain.

For one, a Synology box won't get into the habit of restarting for ten minutes daily because Windows Update managed to break itself and keeps retrying the same update.

But it's true that you could probably leave a desktop on "NAS duty" for years unattended without anything really major happening, especially if it's only accessible on a local network.