Well there is one thing. He did conquer most of the known world. I suppose yea, his father was the one who set up the army, but i highly doubt his army was so strong that it could steamroll over everybody without any actual leadership and guidance. Also i highly doubt macedonia had the strongest army ever at that time and that alexanders enemies didnt have anything. Someone had to have a severe inpact. If not alexander than someone else. Also about his empire collapsing right after his death. He had enough time to conquer, not make sure it would maintain and govern. Unlike Charles the Great, who spent half his life invading and other half basically governing what he ruled.
nobody argues the fact he conquered most of the known world and led his army, but i argue the fact it was as hard as people are trying to show; his army was prepared by his father, his army was undoubtedly the strongest, highly prepared, heavily and well equipped, if i remember correctly macedonian hoplites had even longer spears than greek's ones, his enemy, if not anything, were still really close to shit (persia was a long dead empire, which army never really came out as outstanding if not for the number, greeks after peloponnesian war never really came out again, and, eventho he had to "reconquer" them, the greeks were conquered by philip) and about time yes, i can't argue with that, but i believe that a weak man, after conquering persian and its gold would have done what alexander did, followed his lust, while a strong man (not necessarly great) would have stopped and started ruling over his empire;
i always believe a contextualization is need everytime and, yes, he was leading his army, but that's a thing that many good generals could have done (as i said he was there at the right time and at the right place), therefore it's not something that qualifies you as great; and for sure keeping your army fighting new enemies and conquering territories recklessly until your very army mutiny and force you to go back surely doesn't either.
before people could rightly argue with the fact that napoleon too didn't stop when he should have so i shouldn't consider him a great general/leader, he's great because he faced certain nations as russia spain sweden portugual netherland prussia england and austria in his time :/