Well, One of the major reasons for the success of Alexander was his well, incredible luck. He was lucky in Persia, yes he did utterly defeat the Persians always as he faced them, however the reason why his army could blitz through the Persian Empire so fast was that he avoided long sieges due to favourable circumstances (or in non-vulcan: luck ). Also, due to the Persian roads he also could rapidly move against the next enemy city... and, the Macedonian army had very fast marching speed. The Phalanx pikemen could march fast, since they carried very little.

In India things would probably be different, he would probably never complete any kind of significant conquest in there, IMHO.