I've read the book, but don't own a copy. My notes from it detail how Smith repeatedly took Grant's side. Maybe I just don't like your use of the word "pivotal," but you seem to be indicating that Buell's three divisions were less important than Wallace's one division.
Who you should really be criticizing are Grant, for stating that Wallace was a coward and that Sherman had also told him so. Sherman wrote that Wallace had little hard fighting at any time, but made a good deal of noise, firing his guns into the woods where there was no enemy. No enemy regt was w/i 3 miles of the front and Wallace was in woods to my right rear on Owl Creek near where McDowell was when fight started. He didn't have to move as he was already in a safe place. Sherman and Grant were liars.
As to the "surprise" on page 236, Smith elsewhere admitted that Grant was strategically surprised, but not tactically. So page 236 either refers to a strategic surprise or Smith contradicted himself.
I don't have to "refute" the post claiming that Buell did "save" Grant. That's an unknowable opinion, similar to opinions that Buell did "not" save Grant, that Grant's last line was impregnable, and that Grant would have won the battle without Buell's help. You should take grave issue with that last one, given the military situation.