THE HistoryCHannel did a great forensic analysis of the battlefield in the past couple of years. It pretty much destroyed most of the previous accounts of what really happened.
If I remember correctly, they concluded Custer died in the first ten or fifteen minuts.
And you are correct, Custer and much of the leadership fell early, which led to a complete loss of command and Control of the battlefield. It was the key thing to the massacre of the 7th.
SNIFF! You...you mean the Robert Shaw version of Custer was WRONG???
Custer's commanding officer, General Terry, offered him the use of two of the deadliest weapons invented in the 19th Century, he refused them, and told Gen. Terry that the 7th Cavalry could do the job alone. So he never took the machine guns he was offered. (Colt's patent Gatling guns). Had he taken them, one wonders what the outcome would have been.