I don't really get that.Best way to updated to 10 is to update to 10.0.0 (maybe .0.1) Then go for 10.3.x. That's how I updated.
If you were an average user, with a stock phone, locked bootloader and absolutely no clue of what rooting a phone means, and for some reason you happen to still be on 9.0.16 or 17, the OTA would update your system straight to 10.3.3.
So why would it be any different with an unlocked bootloader or even root?
Having an unlocked bootloader forces the updater to download the full rom, instead of the incremental update, meaning there should be even less of an issue.