It's all well and good to say that, but the fact is that with catching prospects, because of their skill sets, most of them can't slide down the spectrum like other players.
If a normal SS can't handle the position but can swing the bat, no problem, slide him to 2B or 3B. Their value isn't entirely dependent on their position. If a 2B or 3B can't handle that position but can hit the ball, slide them to CF. And then to a corner... and then to 1B.
If a catcher can't handle the position but he can swing the bat, for most catchers, he better be able to swing the bat like a motherf***er because all of a sudden he's a f***ing first baseman where a guy like Miguel Cabrera can be the f***ing 5th best hitter at the position in any given year.
Catchers who can play anything other than C or 1B are a rare breed. Maybe Pentecost can do that, Carlos Santana is an example, but it's very unlikely.