I've did some testing to clean install the same latest version FW today.
Hard reset via setting or at boot or wipe via recovery won't give a clean install, whatever system apps you've deleted previously stays deleted. Root still stays if rooted.
Adb sideloading will clean install the FW back to factory stock.
Ota won't work if rooted. Unroot to get ota also cannot.
So stay rooted, download latest FW to root folder and let phone detect the update. Root stays, everything stays. If you unroot and update, everything stay but you cannot root back after update. Then you have to reset/wipe and root again.