… I dunno. He commanded at most 200 men… ever. (“Apache Pass”, 1862). He was wily, to be sure, but compared to pretty much any battle worthy of the name, he was thumb-wrestling.
To be fair, Medals of Honor were easier to obtain in the Civil War but I think you make the case that Custer was shall we say fearless in battle and reckless and petty as a commander. Is he good, no but far from worst. There are many of his contemporaries that I would argue as far worse. Benjamin Butler anyone? And yes the credit goes to Grant who led a masterful campaign to grind the south down.
So the size of the army defines a great general? I’m not saying you are wrong here but all battles in the west were small. Little Big Horn had what 6,000 combatants? It was impactful for the Indians but a minor Incident in the history of the US. It was a different kind of war with large areas of terrain and small people. I guess Cochise would be considered a raider rather than a general. But Custer commanded a small unit which probably disqualifies him also.
And yes I’m focusing on American commanders not because we are best or worst just because I can discuss them more than some others who may be far better or worse.