There is a difference between a prediction and a projection. But, throwing together a prediction based solely on RPI, isn't a prediction, it's just a lazy way to throwing together a bracket. If you're going to "predict" a bracket, have some kind of overarching foresight of all the conference battles, and make an educated prediction.... you owe that to yourself and everyone else who is going to look at it.
If you're not going to make a decent educated prediction, ATLEAST use the correct seeding method to give everyone an accurate PROJECTION. and if you can't do that, I suggest just not.