A rooted computer is the opposite of a black box. This makes no sense.

Rooting gets you additional means to reverse engineer the proprietary software system but doesn't automagically lighten the box.

It's all relative of course, maybe you view anything you can Ghidra as not-black-box. (though this is kind of tangential to rooting - for a many/most devices you can get a hold of the blobs to reverse engineer without rooting anything)