From the moment of introduction, it was quite obvious that these two charismatic men would not get along. Aside from the romantic competition centered on Millerna, there was also a certain amount of professional rivalry in the matter of team leadership.
Van was an able fighter, but he sorely lacked Allen's knowledge of military strategy and politics. In turn, Dryden's understanding of history and human nature proved quite useful in deciphering the secrets of Atlantis and in forging necessary alliances. Pride and arrogance prevented both men from easily yielding the mantle of leadership to someone more qualified. Moreover, once it came out that Dryden was a fervent admirer of Allen's estranged father, there could be no partnership between them. The situation became quite fuzzy in the later episodes, so no real resolution was achieved. I would like to see Dryden's triumphant return, if only to have the pleasure of watching a battle of witticisms and insults at court.