Re: Bending the wrist and tailing loops
I don't know what the author was thinking either, but all I can guess is this: that a lot of wrist in the backcast can result in a wide loop which doesn't ever straighten because the fly leg momentum is not directed backwards. If no forward cast were attempted, the line would fall in a pile cast.
But with an attempted forward cast after such a backcast, when most of the slack in the line is taken out, then the rod is shocked all at once from the load, the rod bends but the caster can't accelerate enough to keep it bent, so it starts unloading too soon - creating the concave tip path you mentioned and consequent tailing loop.
How common this is I don't know, since most people with windshield wiper backcasts have much the same for the forward cast. Jackster would know, as he has a lot of experience as a casting instructor.
The audience which that article was intended for was newcomers, so I think the author was trying to impress the importance of a stop without wrist movement.