Having a great big man is more likely to lead to success because baskets inside are the highest efficiency shots you can take. If you have a guy on your team who can get 20-25 points in the paint at a high percentage (50+) every single game, you are in a great position to win. On top of that, if you have a great rebounder, you get more chances to score and your opponent gets fewer chances.
Basketball is a pretty simple game...whoever gets the most chances to shoot the ball and also shoots it with efficiency is probably going to win, and no type of player makes it easier to do those two things than a dominant big man.
Transcendent point guards are great, but the fact is this is becoming more and more a guard-heavy league. It's always been hard to find great big men, and it is harder now than ever. It's not that hard to find a point guard who can run things tolerably well. Also, if you get a great big man, even a merely decent point guard can look great (e.g. Felton).
So yes, given the chance, I would trade a great point guard for a great big man, even assuming equal talent. In this case, I don't think there should be any question that Griffin is an all-time talent - a true franchise cornerstone. Barring major injuries, he should be in the top 10 players in the league, if not top 5 (he may already be top 10).
I wouldn't be altogether shocked if Rondo never cracked the top 10, due to his being a somewhat limited player.