[Texas Mulerider]

Had Lincoln fired McClellan early, it would have been a very different war.

Quite possibly. I suppose it depends on the replacement. If Mr. Lincoln had recognized Grant's talents early on and moved him east, then I suspect you're right. But replacing McClellan early on with, say, John Pope wouldn't have made much of a difference, IMHO.

[Non-Sequitur]

But replacing McClellan early on with, say, John Pope wouldn't have made much of a difference, IMHO

Or Burnside or Hooker for that matter.