Turning a device off is essentially the Reboot action, unless you're using a sledge hammer to hit the power switch. And FWIW remapping the function of a Power button on a device is absolutely something Malware and the like do all the time IRL. If Stuxnet can do it, so can Black IC I should think. Modern devices do not have an electro-mechanical switch like a light switch. You are not mechanically completing or breaking an electrical circuit between the power supply and the CPU.
I've always presumed the Jack Out test was because its a pressure situation where seconds matter. You need to first recognize that you're Link Locked. Two, know what to do about it. Three, actually do that thing in a couple of seconds before the terrors from the digital realms fry your brain and call down a drone strike on your meat body.
If effectively no test is required to break Link Lock, what's the point? Link Lock forces a Persona to stay on the Matrix so GOD can rain down righteous retribution on the Hacker via digital demons. Jack Out is the frantic, last second scrambling to prevent that.
You can fluff the Jack Out action however you'd like. Yank the batteries, manually turn off the Wireless, deliberately crash your own OS, whatever. (I have no idea what the Technomancer fluff would be...) I'd even let other PCs assist with the appropriate rolls. But it's still a roll, because the PC can fail, and there are serious consequences for failure.