I think maybe he tried to do too much with them and was just too... ambitious. Like his ambitions for the characters outstripped his ability. Saying that though having that number of characters introduced should be possible. We managed to learn about Stiles and Scott and Melissa and the Sheriff and Derek and Peter and Lydia and Jackson and Danny and the coach and Chris and Allison relatively quickly in the first season so it can be done, introducing that number of characters quickly, I just don't feel like they have been integrated or developed enough. They do things and we have no idea why other than "because they are evil". And that's not enough. Peter was evil because of pain and revenge. Kate because of her beliefs. Gerard it was due to his philosophy and revenge - initially - but then it twisted around to be about trying to escape death, about his own narcissism and hypocrisy. Matt because of revenge and early trauma. The alphas? They just wander round peer pressuring alphas to kill their packs because of reasons.