In reality, George Armstrong Custer was the finest Cavalry Officer that the US Army ever produced. The fact that he had the poor luck to be killed along with his men is what has allowed the survivors to heap all of the blame for the disaster on him, when in fact he was poorly served by a number of Officers in his command, and arguably, had they chosen to vigorously support Custer, the disaster at Little Big Horn might well have gone very differently.
And it was still Crazy Horse, not Sitting Bull, who led the attack on Custer.
Have you ever read a bio of the man? I’d suggest you do. He was horrible. By todays standards he’d never have been made an officer and on any one number of occasions his conduct would have had him court-martialed. Had he survived the Bighorn he would have been.