I actually thought Datone started to come into his own as a DE in the last half of the season. He's been dinged a little in the past, but I thought he showed marked improvement. Daniels is a nice rotational player also and I think the reason you saw him wear down later in games is probably the fact that he was playing too much. He showed some real talent the last two seasons though.
I do agree though that we need to upgrade some talent in the interior DL. We have a collection of good rotational players (Daniels, Raji, Jones, Boyd) and I'm optimistic that Pennell can become a similar rotational player. We need at least 1 elite player in that interior though who can consistently win 1 on 1 battles.