No, this cannot be considered entirely safe due to FRP.
It may be safe for OnePlus devices, it depends on how the OEM has implemented FRP.
FRP is an anti theft measure, that basically bricks you device, until factory reset is confirmed by the owner.
That means you need the login information, to confirm the factory reset when the device is rebooted.
This should not usually happen, if you make the reset from the settings menu when logged in.
But if you make it from bootloader or by button combination, you could be in trouble. androidcentral.com/factory-reset-protection-what-…
The entire FRP idea is incredibly stupid, because there is a workaround, which of course criminals learn to use routinely, but can be a major inconvenience for legal users, and may even mean permanent brick for non techie users.