Your presumption is very reasonable. I remember that a dev mentioned that the player became the inquisitor very soon at the beginning but that looked too simple, so they changed the plot and added "in your heart shall burn" to make sense. ( Damn I've forgotten who and where! Can someone provide the link?)
Evidence: In the game there are chances that you are called "inquisitor" in Haven due to some bugs.
And our poor Cory has to stand on the stage too early, losing mystique.
I don't think he necessarily loses mystique in that regard.
If In Your Heart shall Burn was late edition, then we would meet and learn about Corypheous when we find out about the Elven Artifacts and the Eluvian connection, which was indeed much later in the game.
So late, actually, that it would probably be a repeat of the complaints on Meredith.
Truth be told, you are right about him being behind the scenes, orchestrating a lot of events to achieve his goals. Notice the only times he is directly involved in something it is due to someone thwarting his plans.
Think about it for a minute:
The Conclave explosion nearly worked, but due to interference it forced Corypheous to find a way to capture the Inquisitor.
He would then have two factions more or less try to capture the Inquisitor, which would fail.
He would take matters into his own hands and attack outright Haven with what he has left. This also nearly succeeds but fails at the last minute against the Inquisitor.
He would then divert his agents to continue their plans, while he searches for the Well. His plans include forcing all Grey Wardens under his charge, assassinating the Empress of Orlais, and causing mayhem wherever possible for the Inquisition to distract them from his true goals.
When the Well is taken from him, he decides to just force your hand and assault the heavens on his own.
All of these actions are more or less happenstance because the player interfered, otherwise he would have succeeded in taking the Wardens, Assassinating the Empress, and using the Anchor, and no one would have known it was him. Basically, he got unlucky because of the player, and chose to act to remove the player, first subtly, then by force.
I don't know, we can't really have it both ways, because it's very possible people would be saying he didn't act enough if we didn't see him that early in the game being pro-active against you. And let's face it, Corypheous personally doesn't have to focus on you at all, he has his minions do it for him while he continues with his plan.