I agree with the fact that he was better than Howard, but the organization looked at Howie as their guy. Mrazek wouldn't have been traded if that wasn't the case.
With Howard being 35 years old now, it's inevitable that a replacement will need to take over soon. Unless Yzerman says we're addressing our future goaltending by FA, this is the time for our young goaltenders to show their worth.
Mrazek was moved because he couldn't find any real level of consistency, was looking to be overpaid for how he was playing, and was a bit of a hassle off the ice to boot. If any of those things had been different, I wouldn't have been surprised if the Wings had kept Mrazek and kept giving him chances, but the guy was a horrible combination of those three things while he was here.
He looks to have finally found himself in Carolina, though. Which is good to see.