Rizzi: Rattler and Haener will compete in practice to see who starts vs Commanders

Yes and No. If it's just for the public, sure. But if they really don't know at this point of the season who they want starting then they should be unemployed when the season is over.
That's simply not true. If they both have their positives and negatives, who you go with isn't always obvious. That's true with a lot of things. Making decisions like this isn't an exact science, and if they're close, you give consideration to both.

That said, I tend to think it's more about not tipping off the opponent as to who you're starting. There's not a big difference between the 2, but I think you have more game film on Rattler, so the defense would have a better idea how to defend him than Haener who has a more limited body of work to pick apart.