Juin, your examples from the Civil war do not cut it. 99% of the US Generals were just friking military morons. The troops they lead had their officers elected, even their senior officers.
Lee was a 1 trick pony, had no idea of a overall strategic plan. Had only 1 solution to a battle. The Union Generals, should have not made Corporal.
The incompetence of military leadership in the civil war is just epic, including the troops.
The one who finally got it was Grant, but the rest are just pretenders, actors. From the military side, that war is a embarrassment, of incompetence and nothing more, costing 100 of thousand soldiers their lives.
Nothing to be proud of.
Even in the 19th century the long practiced principle was to recruit willing Soldiers, train and treat them well and have leaders that care about 'em and their well being. In contrast of course badly performing armies as we are witnessing of the Russians in Ukraine are composed of unwilling conscripts who are poorly treated and led on top of being inadequately armed and equipped. The "don'ts" are exactly Russia in Ukraine ain't they.
The Union mobilized more than ten times as many Soldiers as in the 2-year Mex-Am War and when there were only 20K professional Soldiers in 1860. The sudden huge number was simply beyond most high-level commanders. Coordinating the vast armies was challenging to say the least. Almost all volunteer regiments were state militias that had never been part of such a huge (Union) force and had never served much less fought as an integrated part of a unified command across all (Union) state forces.
Offensive operations into enemy territory here and there were also extremely difficult logistically although the Union got greatly better at it after Lincoln appointed the masterful logistician Gen. Charlie Halleck as chief of staff -- Halleck who was regarded as an intellectual and who many call brilliant got supplies and reinforcements exactly when they were needed and where. The conscious exception was Sherman who would not risk depending on supply lines through GA and to the Sea, having his many troops forage off the land and its farms, towns, villages. With Sherman's 60 mile wide swathe across GA his mass of troops were well fed and on the spot; Sherman commanded his sprawling and steadily advancing force superbly.
The Union's early problems were somewhat similar to those of the USSR in 1941. Stalin had to rapidly and hugely expand the size of the Red Army while also having lost a good number of the officer corps -- in the Union's case caused by abandonment, in the USSR the prewar purges that put junior officers in command of large units. It's challenging to know who will succeed and who will fail when lieutenant colonels and majors are necessarily thrust on the spot into becoming brigade and division commanders.
Grant's great and determined success in the West, ie, the Mississippi River Valley states to include New Orleans, caused Lincoln to advance him to General in Chief of all Union Forces. (Whatever brand of whiskey he drinks, Lincoln proclaimed, send it to all our generals!) First thing Grant did was send the incompetent officers to the West where Grant and Sherman -- and the step brothers Adm. Farragut and Adm. Porter, sons of a Navy Commodore father -- had well settled matters. Concomitantly Grant advanced new commanders to his forces in the East based on reports by their units. As I noted in scrolling, Grant was given full authority by Lincoln to win the war which he and Gen. Sherman restrategized and proceeded to do. There's a fascinating book:
The Friendship That Won The War.
Another immediate move by Grant was to advance Gen. Philip Sheridan to command of Union cavalry which had been far outclassed by Confederate cavalry and the likes of Gen. Bedford Forrest among others. Sheridan in turn advanced the Michigan boy Custer as his primary (lead) division commander, which is a remarkable story given the hard and fast riding General George Armstrong Custer had started the war right out of West Point as a cavalry lieutenant troop leader. So as the saying goes, when you got it, flaunt it. As Potus, Grant appointed Sherman as General in Chief of the Army and chose as his in turn successor Gen. Sheridan who Grant always said was the best general in the Army.
Post Civil War and to correct shortcomings the Army established its War College and also the Army Command & General Staff College, among other colleges of advanced studies of command in war and peace.
Your post is very harsh given especially German generals have lost two world wars. In the same half century besides. After causing both of 'em of course.