I don't think this is true. If you have Verizon for your carrier, for example, it doesn't matter where you bought your device, from Verizon or Google unlocked, the updates aren't available any sooner for the unlocked version because ultimately the carrier has to approve before you will get it. My fiance has a Google purchased P7Pro and I got mine from Verizon, yet neither of us got the update via OTA until yesterday afternoon, when everyone on Verizon could get it. The version you have from Verizon on my Verizon purchased device is exactly the same as someone who bought the same device from Google. I've had Pixels since the OG 1XL, all purchased from Verizon, and I know others who have the same devices from Google and I always got my update the same version and day as them. The updates come from Google initially, but it is the carriers that "allow" them to go through to their customers regardless of where they bought their devices.