Williams is far from perfect. I think he is sloppy and has a lot to learn. There have been better DTs in the last five years. Williams doesn't look like an instant impact guy to me, unless he is real good at taking to coaching. He plays high and is inconsistent with his hands. He lets Olinemen get inside leverage. He has ability and measurements but most talk like he is the next great. I'd take Suh or McCoy coming out over Williams.
I cannot believe the Titans think Mettenberger is the guy and even with questions about Mariota he is still better than Mettenberger right now, when comparing ability. They should not pass up the QB. No team should pass up a QB if that QB looks better than what they already have. Even if it is very close to what you have, take the QB, because it is hard to measure intangibles and they are what often puts QBs over the top.