There's so much disagreement about who is to blame for what happened at Little Big Horn, and it's very hard to find completely neutral books on the subject. The author usually has an angle. Personally I view it much the same as Isandlwana - there were a lot of ways to lose the battle and the various actors found one way of doing it, but the buck stops at the commanding officer, both for the dispositions of the troops on the day and the divisions created in the staff and field officers in the weeks leading up to it.
Of course, relatively people actually credit the Sioux (or Zulus!) for making each action virtually unwinnable for their enemies. As soon as the decision to attack the camp was made, I don't see how Custer could have come out with a successful outcome, although it's perhaps more a case of whether he could successfully withdraw his command largely intact or whether they all would be lost.