We had one of your chorbishops visit once. He explained his status as doing the job of the bishop but with none of the rights/powers/privileges of the bishop.
Btw, as I have contended elsewhere, the presbyterate arose out of the chorepiscopate.
Are you sure the presbyterate itself rose out of the chorepiscopate, or do you mean that the "independent' ministry exercised by presbyters rose out of the chorepiscopate?
And I think I know which chorbishop of ours you're talking about: he's a character (
), his explanation (not terribly accurate) doesn't surprise me. Chorbishops nowadays are basically "archpriests" (an award). They don't have any extra authority unless specifically delegated (ideally, they'd function like deans of regions within dioceses). But they do have some ancient canonical prerogatives (e.g., they can ordain chanters, readers, and subdeacons) which they almost never exercise because they require episcopal permission. In other words, today they're basically pretty priests.