Originally Falcon (and Peregrine I suspect) did not support Factory Reset Protection
(FRP) - this may have changed for those with locked Bootloaders who updated to Lollipop via official OTA Update. Even with FRP, all you are doing is stopping someone who stole / found your phone from accessing your data. Obviously you must unlock Bootloader to gain real control over your data by flashing a ROM just as those created by @minimale_ldz
. Once Bootloader is unlocked, it's permanent. So-called 'relocking' is purely superficial and can be simply undone by anyone with fastboot access.
So the answer is no, flashing Stock Recovery and 'relocking' Bootloader does absolutely nothing for you in terms of security.
Newer phones such as Moto G (3rd Gen) support FRP out of the box. But again, you are at the mercy of Google and Motorola when it comes to privacy as long as the Bootloader remains locked. You cannot root, nor install a custom ROM.
I fear ultimately you must examine your own psychological / egoic need for control and privacy, as the world outside your mind is unlikely to deliver what you seek.