Off the top of my head Gus MacPherson was promoted from within and he did pretty well for us, we could trade individual examples or accept there are no guarantees when selecting a new manager - I'd still prefer said No2.
My real irk is the line you didn't quote
I'm speculating but say, for example, Ryan Flynn has done his coaching badges, I'd rather take the "punt on an unknown quantity" on him with, of course, an experienced No2.