Bookworm, the max coeficient of lift / rate of turn ratio is not a constant. It depends upon the design of the wing, the distance between the centre of lift and the centre of gravity, the airspeed and a great many other factors. As has also been stated, it is not appropriate to assume a constant angle of bank. The maximum roll rate of the aircraft is a major factor here as well.
What, as I read it, that article is highlighting is the inherent dangers of attempting to carry out such a maneouvre without having practiced it in your current type when other, far less dangerous options are usually open to you.
I have only once seen a pilot attempt to turn back to the runway after a power loss (it was not total) on the climb-out. He made it back to the runway (just), but the aircraft was a total loss. And this was an experienced pilot who (in my opinion) should have known better.
I know that the RAF certainly used to teach turn-back techniques (I don't know if they still do) but it is not something that should be attempted for real unless it has been practised.