I suspect the attributes a winning general was expected to have didn't apply to Grant; he was no Halleck or Hardee who both wrote manuals on military tactics/war or no McClellan who had his well trained army but was afflicted many times with "a dose of the slows". In boxing terms Grant,perhaps,was more like a Joe Louis type of boxer - going forward to seek out the opponent - "he can run but he can't hide" - with all guns concentrated and blazing away at the target.
Charles Francis Adams was the US minister to the UK between 1861-5 and whilst there his son Henry acted as his private secretary.
The autobiographical work "The Education Of Henry Adams" contains this appreciation of Grant and Lee.
Adams did not feel Grant as a hostile force; like Badeau he saw only an uncertain one. When in action he was superb and safe to follow; only when torpid he was dangerous. To deal with him one must stand near, like Rawlins, and practice more or less sympathetic habits. Simple-minded beyond the experience of Wall Street or State Street, he resorted, like most men of the same intellectual calibre, to commonplaces when at a loss for expression: "Let us have peace!" or, "The best way to treat a bad law is to execute it"; or a score of such reversible sentences generally to be gauged by their sententiousness; but sometimes he made one doubt his good faith; as when he seriously remarked to a particularly bright young woman that Venice would be a fine city if it were drained. In Mark Twain, this suggestion would have taken rank among his best witticisms; in Grant it was a measure of simplicity not singular. Robert E. Lee betrayed the same intellectual commonplace, in a Virginian form, not to the same degree, but quite distinctly enough for one who knew the American. What worried Adams was not the commonplace; it was, as usual, his own education.Grant fretted and irritated him, like the Terebratula, as a defiance of first principles. He had no right to exist. He should have been extinct for ages. The idea that, as society grew older, it grew one-sided, upset evolution, and made of
education a fraud. That, two thousand years after Alexander the Great and Julius Caesar, a man like Grant should be called--and should actually and truly be--the highest product of the most advanced evolution, made evolution ludicrous. One must be as commonplace as Grant's own commonplaces to maintain such an absurdity. The progress of evolution from President Washington to President Grant, was alone evidence enough to upset Darwin.
Perhaps Grant was too simple to be understood by folk from a different background - such as Henry Adams who after all came from a family which had a presence in US politics since the Revolution.
I'm a Big fan of Grant the fighter.