Yes he did... but he did more good for the South with his alarmism.
Pinkerton was a very cautious man who always overestimated his opponents. But I don't think McClellan would have taken advantage of even totally accurate estimates of enemy strength if he had them.
McClellan was a wonderful parade ground general. He could train troops to be 'the best they could be.' But as to battlefield tactics, he totally sucked. He was overly cautious, not for the sake of the troops, but for his own reputation -- which was all he really cared about.
The only good thing to be said is that he did train the best army the world had ever seen at that point, and US Grant finally utilized that army to its full extent and ended the war that McClellan could have ended two years earlier.
Salute to the Army of the Potomac! They were good soldiers and the best in the world when they finally had a great leader in General Grant.
McClellan was certainly overcautious, ridiculously so. But I do think that at that time, no one really appreciated how bloody the war would be. Except perhaps Sherman, who was written off as crazy for his prognostication about the number of troops the North would need.
If McClellan had entered into a confrontation resulting in the kinds of losses that Grant later experienced in several of his battles, he would have been removed from his position and vilified by the northern press.
The web site points out that, at the time that McClellan was moving so cautiously up the peninsula, the battle of Shiloh was about to take place. Shiloh’s losses were a shock to a lot of people, north and south. But the people would be in for a lot of such shocks in the three years ahead of them.