Gain full control over my device

Your dm-verity is fucked, can be fixed with adb

the botnet (Google) is trying to scare people who dare to reclaim their digital sovereignty

Because the device won't know if you gained full control or someone else.

They wouldn't bother, they know those people wouldn't be put off by such warning. These warnings are mostly for legitimate and legal reasons.

Unlock bootloader faggot.
Red means bootloader is locked and invalid signature
Yellow means custom signing cert
Orange means unlocked bootloader
Green means locked bootloader
If you want more security and a message that takes less time then try custom AVB certs (yellow).

What the flying fuck is this

Plasma mobile

This.

KDE is nice but it needs a pretty fast computer to be smooth. I'd hate to see how it performs on an average phone.

Translation: A modification not authorized by the manufacturer was detected. If this wasn't you, you should be very worried.

wow it's almost as if having every facet of your digital life tied to one always-with-you device is poor form

The only problem is that many people who root are 13 year olds who want to impress their friends and then install modules and tweaks they don't understand.
Android and iOS normally have a thick sandbox in place to keep applications from meddling with other applications. Jailbreaks and Roots throw that out of the window.

If you only install root modules that you've written or audited yourself, there would be no problem. But nobody verifies that. Do you honestly think you can trust those developers? Even Apple and Google occasionally fail and let malware into their stores, but at least it can't do that much harm thanks to the sandbox.
But applications that run as root? Kernel extensions? From complete strangers? Nope.

You might just as well run an OpenSSH Server on your device with a standard password for root!
... Which current iOS Jailbreaks even do, without ever telling their users, unless they happen to know what OpenSSH does and clicking the package in their Jailbreak app store and then clicking one of the sub-links that explains how to log into their device with SSH and what the default password is.
It's "alpine", by the way, so if you want to pwn retards with Jailbroken iThings, feel free to spam that to every device in your local free network of choice. You'll be rooting jailbroken shit left and right , user promises.
And that isn't even the malice, that's just the jailbreak community's incompetence.

I also want to own my device. But I certainly don't want to give random criminals all over the world root access. Luddites who aren't even aware of the security implications can't be trusted to get root access to their devices at all. And that's what this warning is for: To warn those people of what they just did. Except it's worded very, very poorly. But they simply don't have more space since the normie's attention span is that low.