The real issue is why the long landing occured and was not noticed by the FO and the go around not called by the Captain.
I agree but,
According to the QRH, using F40 for landing only saves a few hundred feet of runway over an F30 landing. If the FO, had no experience of F40 landings, a wet La Guardia, was not the place to try it
the above doesn't wash with me because the Captain wanted to do a flap 40 ( ie his experience told him it was the best flap setting for the conditions), and, if there is a chance of tailwind in the flare flap 40 results in a better touchdown point, and, they only over ran by the amount the QRH says is the difference between 30 and 40.
That said, I agree with you that the primary problem is the lack of a go-around.