With respect the same, I never said YOU said that, but Fuller said it and you repeat it, presumably because you are trusting Fuller.
The point of Fuller's thesis is that Grant was thought to be a "butcher", and he has gone out to prove them wrong. The only thin worth disputing book-length is something commonly believed, and it was not commonly believed unless you were a total Unreconstructed nutcase.
Please name the popular, non-memoir or not Southern-fringe titles up to 1929 that believe Grant was, per Fuller, "quite unjustly...been handed down to history as a butcher of men," or that "Even [in 1929] they have not lost their sting; for in the opinion of many Grant still represents the butcher type of general." I don't know what they say in Britain.
As for that Lost Cause thing, you are repeating Joan Waugh's thesis. Her idea that the Lost Cause toppled Grant and replaced him with Lee is so ridiculous its literally funny. Need I mention Grant is buried in a huge mausoleum with a Sistine Chapel painting at the top while Lee gets a tiny chapel (smaller than every church parish I've been member of) with some ugly velvet painting mounted on the wall. Again, there is no proof that Grant was "unpopular" up to Fuller or after, given the works written. in fact its the opposite.