The list of corps commanders killed or wounded at the front reads like a who's who of the Civil War. Are we to assume Jackson, Longstreet, McPherson, Hancock, Sedgwick and a number of others were poor corps commanders because they were leading from the front? I have questions about the capabilities of some of these individuals, but the presence of a corps commander at the front seems to have been fairly common.
Not necessarily - it's not the
only thing that matters about a commander - but it actually is a point against them, depending on the circumstances.
Jackson and Longstreet both got shot by their own men, which is essentially a mishap in what they could believe to be "safe" territory. They were not endangering themselves unduly.
Hancock, meanwhile, was knowingly exposing himself to danger as part of keeping his men steady. He knew about the risk, certainly, and judged that the benefit (of keeping his men steady) was worth it; he was within his own line of battle, and at a time when the main thing his corps needed to do was to withstand fire. This could be considered to be a mistake
if the possible risk of losing the corps commander did not make up for the benefit.
Sedgwick, likewise, was within his own line. The nature of his death suggests that he was hit by what was essentially a random bullet; he did not unduly expose himself to danger.
McPherson was possibly at error for not having a sufficiently large escort. The area he was shot in had previously been "rear area" territory for the Army of the Potomac and he could believe it to be safe.
What Reynolds did was to ride at the front of his men during an advance into enemy territory (high risk) and there was no significant benefit that accrued from this. That's why it's a point against him.