Actually, Custer was not an inept general. However, he was IMPETUOUS, a trait that has made or broken some generals. During the battle of Gettysburg, Custer impetuously led some 500 Michigan cavalry troops in a charge against Confederate General J. E. B. Stuart's 4,000 mounted soldiers. Custer managed to cause an immense traffic jam in a fairly narrow riding lane that prevented Stuart from attacking the center of the Union line from the rear. had Stuart succeeded, Pickett's Charge woulda overrun the Union center, enabling pickett and the rest of the Reb army to roll up each flank of the Feds. In the chaos which resulted from Custer's charge, Stuart had to order a retreat to re-organize hois troops. Custer wisely made a hasty exit with his men after that charge until more Fed cavalry arrived.
Custer graduated from west point last in his class of 34, in 1861, and was quickly pressed into service in the Civil War as a lieutenant. At first, he alienated the men under his command with showy uniforms and "fancy" hairstyles, but he soon won them over by his willingness to lead attacks, rather than just sending them forward and then hanging back. He told them his uniforms & hair were so they could easily see him and follow him, & that he was counting on the enemy's poor marksmanship to survive.
Custer impressed the Army of the Potomac's cavalry commander, Gen. Pleasonton, who brevetted him to brig. general. During the Civil war, his headlong charges were made only after careful planning, so they served him well. And there's no denying Custer was a "publicity hound".
After the war, he was reverted back to a captain, & considered leaving the Army. But the ongoing battles with Indians, and a lack of civilian jobs that interested him convinced him to stay.
His "last Stand" was a result of his failure to do a thorough recon job, for once, thus not knowing the size of the Indian force before him, and failing to recognize the fact that the Indians were well-led, well-armed, and were better marksmen than first thought. it's conceivable that Custer's vastly-outnumbered force could've succeeded, if not for Crazy Horse's quick reaction to Custer's attack and skillful leadership in countering it. Custer hadn't believed the Sioux capable of any ORGANIZED counter-attack, and thus was defeated.
Custer's first big mistake was his last.
Had Robert Lee not suffered a heart attack and still had available the skills of the autistic Thomas "Stonewall" Jackson the south would not have been defeated at Gettysburg.
Custer was basically as self serving jerk who lead four family members to death - Harry, Thomas, James, and his youngest brother Boston.
One of the saddest elements is that Sitting Bull was ignored:
“These dead soldiers are the gifts of Wanka Tanka. Kill them, but do not take their guns or horses. Do not touch the spoils. If you set your hearts upon the goods of the white man, it will prove to be the downfall of this nation.”
He was right - the backlash from Big Horn eventually destroyed not only his people but himself.