Side-loading is just as "legit" its just loaded differently. I guess if your scared of it just enjoy the soup line and happily wait to be spoon fed your update. I always feel pity on those not confident enough to take control of their devices.
FYI Side-loading has no danger of bricking your device. Your device is meant to be able to do it. It is literally designed for it. Side-loading is safer since it cant get corrupted by WiFi.
Oh, don't 'pity' me - not afraid of jumping the queue when its necessary. And I can handle sharp sharp cutlery, too - not just wait to be spoon fed. But really, this is far from necessary. Its an upgrade (not a critical patch) to a device that isn't even my secondary bit of daily tech kit.
Meanwhile, I have done minor sideloading - for example, Flash onto my Nexus 7 (if only so I can access TV streaming websites via Firefox that have not yet built an Android app), but that was completely straightforward and done completely onboard the device.
But to entertain doing sillery-buggery multiple button pushing at just the right moment to access hidden controls and / or wipe my device harkens me back to old Palm days. Layer that with geeky access to Terminal to unpack and then install over to the device and, well...its ain't a priority.
It seems more than a pity that Google doesn't supply the OS upgrade via it's own online Google Play Store, say, along the lines of (dare I say it) Apple's iTunes or Mac App Store. Plug your Nexus into your computer, choose the OS Upgrade and let it all download and install via the Store. Google's servers permitting, this would seem to be a way they could get the OS out to their users quickly - as in as soon as it was announced and released - securely and relatively brick-free, especially if users have sometimes dodgy OTA connectivity.
For users having to wait for Google to choose when the devices should get an upgrade that they are eligible for is bad PR. And it only encourages amateurs and cowboys to do something wrong and / or inadvertently install a wrong / corrupted file.