In that case, big men have statistical variation in how well they shoot too, just like outside shooters.
How many times have you seen a big guy "disappear" or "get shut down" for a game? Maybe their percentage is more consistent but their output can vary widely based on the defense and scoring pace for the game.
The other factor to consider is, how many great big men are there in college basketball? Maybe one per year coming out of high school would qualify as "great," and if he actually lives up to expectations then he'll be gone in a year. Conversely, there are probably 5-10 excellent three point shooters in each class. And Duke gets all of them
So if you're going to build your program around a particular style of play, relying on three-point shooters is more "dependable."
Finally, if you look at past National Championship winners, they all have excellent talent obviously but you can't really make any generalizations as far as them all having a dominant big man, or all having a sharpshooter. I think having solid guard play is probably a safe rule of thumb, but in the end it's overall talent and team play that matter