I am probably like a lot of others in at first thinking Alexander was an absolute genius to be able to conquer a vast empire.
But recently I wanted to write a novel about the Theban Hegemony and started reading about the period, that is immediately before Alexander. And his magic seems to kind of disappear. Some of what at first seems to be his genius now seem like was already in use around Greek military or came up with by his father. That would still mean he's a good learner, but still.
So how good, really, was he?
Oh and what books should I read for my research? I have The Theban Hegemony 371-362, and Military Theory and Practice in the Age of Xenophon
To be honest, the "skill" of a general or in this case the "greatness" of a general can not be tangibly quantified. It all matters on perspective, now and then.
For instance, your hypothesis is correct. The reason why Alexander had a such a smooth, comparatively, ascension to greatness is because he was born onto a military foundation that was more stable and superior than any other military force in the Mediterranean at that time. For the first time in Greece, significant numbers of men could essentially be professional soldiers, the cavalry were put into a place of importance and treated as so, and the military processes were developed to be practical and efficient ("You mean we SHOULDN'T have a long baggage train?"). All this information would imply that Alexander wasn't as Great as he was. It doesn't help that at the battles of the Granicus, Issus, and Gaugamela, which in my opinion won Alexander the Persian Empire, Alexander made a several costly and recurring mistakes (such as neglecting his left wing battle after battle.) Not to mention the blunders and failures that military commanders often faced, but these can be pushed aside as common occurrences when dealing with the art of killing thousands of men with your own thousands of men.
At the same time, Alexander did some "great" things. He did WIN the battles of the Granicus, Issus, and Gaugamela, battles that he should of lost in normal circumstances. But more importantly, he changed the course of the world. For the first time, large swaths of land and populations of people were brought into exposure, influence, and connection with the Hellenic world. This phenomenon, from Babylon to Pella to Rome, in turn created a Hellenistic world that would not topple until the Romans under Augustus did the same thing, in the idea that all of the Mediterranean would be under one influence. The fact that all of this can be attributed, to the actions of a ambitious Macedonian commander from a place generally considered to be full of goat-herders is why Alexander III of Macedon, in my opinion, is great.
If my "perspective" answer above didn't answer your "Is Alexander Great" question, then here is an example of that "perspective" phenomenon at work at a near-contemporary time:
When Hannibal Barca was asked who the "Greatest" Commander was, he responded something along the lines of (though his actual response is disputed): "Alexander or Pyrrhus, then me."
If you don't know Pyrrhus of Epirus was a commander who achieved little to none of his goals and ambitions. He single-handedly managed to irritate both the Romans and the Carthaginians, and was obviously defeated (I mean tactically withdrew). Yet Hannibal Barca, the man who brought Rome to its knees with a ragged-band of mostly mercenaries or non-Carthaginians, considered Pyrrhus of Epirus a man who possessed such military skill to put him right behind Alexander III. Makes you think, doesn't it?
edit: spelling
Alexander the Great, Hannibal, Julius Caesar, Genghis Khan, Napoleon.
Of them only Genghis Khan built his army from (almost) nothing. One can't blame the others for taking advantage of what they had (Genghis would have too).