I think you guys are somewhat exaggerating. Williams' music is music-technically spoken, and often also emotionally, by far Vangelis' superior. Think of Hook, Schindler's List, Superman, Witches of Eastwick, Empire of the Sun, Seven Years in Tibet. Those are scores Vangelis could have never written. On the other hand, Williams CAN write Vangelis like music which is emotionally even stronger than much of Vangelis' own works (I think of Jurassic Park).
Don't get me wrong, I am certainly a fan of Vangelis, but he's no match for Williams (in his Golden Years). By the way, I think Vangelis' March With Me is one of the best pieces of music ever written in the history of mankind.