Sedgwick was the highest ranking Union general killed during the Civil War, while McPherson was the second highest ranking.
Sherman was devastated by the loss of Sedgwick and Grant was shocked by the death of McPherson. If it affected those top 2 generals it must have had shockwaves that reverberated.
I would agree. There were rumors that Lincoln was going to replace McClellan with Kearny. Kearny could have been the man for the job. I love some of his quotes.
In response to the order to retreat after the Peninsula Campaign Kearny responded, "I Philip Kearny, an old soldier, enter my solemn protest against this order for retreat. We ought instead of retreating should follow up the enemy and take Richmond. And in full view of all responsible for such declaration, I say to you all, such an order can only be prompted by cowardice or treason."
Once when kearny led his men he shouted, "Don't worry, men, they'll all be firing at me!"
Shortly before his death when warned to be cautious when inspecting a gap in the Union line he said, "the Rebel bullet that can kill me has not yet been molded."
And Pender was one of the few non-Virginians to have a shot at high command. I didn't include Ramseur and Cleburne because their deaths came so late. Same with McPherson on the Union side.
A S Johnston's death came so early in the war did he have enough of a track record to surely show what his potential may or may not have been? I'm not so sure. Going by their records and time of their deaths when they still could have made a difference I would have to say Jackson and Reynolds would by far be at the top of each side's list.
Quoted from the article,
"Johnston loss was a damaging blow to Confederate morale, particularly for the president, who held Johnston in immense personal and professional esteem. After the war, Davis wrote, "When Sidney Johnston fell, it was the turning point of our fate; for we had no other hand to take up his work in the West."
I think some of the best generals were lost before 62, before anyone could really determine their value, and then were overshadowed by the later generals who won the war. For later years, Stuart's loss was an immeasurable one.