The main thing was that it took way too long to correct the damage of Ned Leeds being shoehorned in.
The saga of the Hobgoblin should stand as an example to all writers that if you are going to make a new mystery villain to have the plan to out them in place, candidate to be the villain chosen, and to make sure that if you leave the story before hand that things will still happen the way you designed it.
100%. Stern would have been better served figuring out a more prominent replacement, in order to make the story more compelling to readers. While, Ned was not a fit for the clues left and had a lame end, I had zero emotional investment or intrigue about Kingsley.