Like most hypotheticals it is hard to say.

Phillip II is credited by many to have built one of the first professional standing armies in Greece. It was fielded full time, and he used it to great effect. Whereas the Spartan army was comprised of the land holding citizen class, and several classes of lesser citizens, service was limited to inclusion in these classes. Philip paid his men a wage, trained them, and equipped them, and had more men to choose from to replenish his ranks. He also changed the Phalanx, as many people know, to include the Sarissa, which is almost a pike. He also employed cavalry with great skill. He then went about gobbling up little cities that were too weak to oppose him, drawing on their manpower and resources to create larger armies.

As a result of these wars, Alexander inherited a veteran professional military, and a Greece that had been decimated by over a century of Greco Persian conflict. He was also able to use his army, his fathers army, to great effect, especially at Gaugamela, where he defeated a much larger Persian force.

But I do not think we can discount Alexander's own military brilliance and daring. I think to answer your question it is entirely possible, given Alexander's talent, that he could have succeeded in his own right, but his father certainly laid the foundation for his accomplishments.