When did the Confederates have a numerical advantage during the Vicksburg campaign?
What I meant was, while Grant had more total men than the Confederates, they were rarely united. There were occasions where the Confederates could have combined faster than Grant could have, had they moved quickly. The Confederates’ best chance was probably during or right after the initial river crossings. On May 1st Grant had only McClernand’s corps and one division of McPherson’s across. But the Confederates were deceived, and Grant never stayed in one place long enough for them to figure out what he was up to. Even after it was more or less clear what was happening Pemberton dithered about joining with Johnston.
Pemberton had just 40,000. They were scattered. Many of them were chasing Greirson. The force you mention consisted of about 20,000 men supported by gunboats. Any real concentration of troops against this force was next to impossible. However, give credit to Grant for knowing this and for also risking being cut off from his supply line for a period of time with this move. It was a bold move.