That's pretty much what Ochoa said in his deck tech. That's not to mention an out against a mirror.
The way I see it, Channel Fireball worked extensively to make sure they were at least in top 8 this year in Worlds. They worked as a team (literally scooping to one another if it allowed the other person to advance) to find the best decks in each format and exploit the meta. They had a variety of decks to choose from for the Legacy/Team portion of Worlds. Of all the decks, they ended up with a simple U/W Stoneblade with some very interesting ways to handle RUG Tempo (which I can assume was the deck they were confidently prepared for at Worlds). It seems if it wasn't for the Dredge match up, David would've had a perfect record.
It doesn't mean that u/w was the best deck for Legacy, but for Channel Fireball, they felt it was the best balanced deck coming into Worlds with a near perfect pilot.

