caseylane, I very much agree with your statement except as someone who doesn't particulary likes Scott I don't see Scott as Derek's Alpha. I don't see Scott as an Alpha at all, but that is another discussion altogether.
Derek, Stiles, Kira and the parents are the main draw fro me as well. Although if derek goes, I go.
I have always considered Derek a better leader than Scott, even at his lowest. To me a leader is not only someone whom people like and follow but also someone who is able to make hard decissions and shoulder the consequences. And Derek does that, often even more of the latter than is his share. And until Scott proves he is able to do that I can't see him as a leader no matter how many inspirational speeches Derek aims our way.
I understand where are you coming from regarding the trio. Derek was in a bad place and desperate but I think it was stated rather clearly that he told them about consequences. I think here also comes into play another difference between Scott and Derek. Derek sees the bite as a gift, Scott as a curse.
Also, there is the other side of teh coin, Derek, who lost his whole family, chose those 3 and offered them something they wanted, needed - family (Boyd), strenght (Isaac) and health (Erica). He was learning as he was going and he was making mistakes but he tried with what he was given. And ultimately he was not only willing to let them go if they decided so, but would die for them. In 3A after he lost his red eyes he became the Alpha he was never meant to be.
As for Isaac's abuse, that is a big issue that is not so much Derek's as the show's. They often treat is as a joke and that makes it hard to empatize in the instances when it's meant to be serious. But that is for another thread.