There are different types of courage. He didn't lack physical courage but he did lack courage in the willingness to look bad. He won 6 of the 7 days battles but retreated every time. If he would have advanced he would have whipped Lee. Hell, he suprised the Confederacy so badly he had Macgruder outnumbered at least 10:1 and should have stompped him on the way to Richmond. He greatly outnumbered Lee at Antietham and had plentiful reserves. If he would have commited them Lee would have been stompped. He might not necessarily have to surrender his army but it would have been devestated.
No, Magruder was never that badly outnumbered. As I discuss
here. Magruder was heavily reinforced before the armies made contact, and the position was stronger in position and numbers than, say, Vicksburg in mid-1863.
The Seven Days battles sees McClellan outnumbered and turned. It's not popular but it is true. McClellan is indeed actually "saving the army".
The question of reserves at Antietam is interesting. McClellan kept a single division in reserve for most of the battle. Initially it's Richardson's, but he releases Richardson to Sumner and grabs Morell's division as it arrives. Later on McClellan releases 2 of Morell's 3 brigades to shore up Burnside.
Franklin's 2 divisions were largely used to relieve shattered sections of his line. 2 brigades of Slocum's division were ordered to attack, but Sumner stopped them and McClellan agreed when he visited Sumner's lines that the line was in such a bad shape he needed the troops to shore up the line against a counterattack.
Incidently, Lee was gathering a counterattack. He had 2 brigades of Stuarts cavalry, 2 unengaged brigades from Hill's division and Hood's division moving to turn the Federal right. It fizzled, mainly due to a lack of Confederate artillery ammunition (they'd already withdrawn their reserve ammunition train over the Potomac).