Succinct, but not true. Gettysburg is a prime example. In each and every battle, victory on either side was determined by the better general combined with the state of his troops moral and confidence. Early in the war this fell mostly to the Confederates. Later, as the Union fielded better Generals and the troops gained confidence in them the tide swung.
You are certainly entitled to your opinion -- though it is incorrect. There were never better generals than Southern generals in the WFSI.
Not attacking up mile-long hills well-covered by batteries may also have had something to do with it....Lee might have learned from the six charges up Malvern Hill that failed in 1862, during the Chickahominy campaign, but then he did it again at Gettysburg. Ouch.
By way of explanation, this was a habit officers on both sides had acquired in the Mexican war, when they got away with assaulting prepared positions defended by infantry and artillery repeatedly, because of the Napoleonic weapons they were facing and the inexperience of most of the Mexican troops. They wouldn't have gotten away with it against Wellington, but they weren't facing Wellington. So they, and Bobby Lee particularly, imbibed a deadly lesson. Thus Edward Bonekemper, How Robert E. Lee Lost the Civil War (Sergeant Kirkland's Press, Fredericksburg, Va.: 1998).