You're exactly right about when you saw Levine. He played dime after Mosley's injury versus the Skins, then against the Giants and Jets in that same dime role. Mosley returned after the bye and we have not seen Levine on defense since except for the final series at cover-2 safety against the Browns. He played some nickel in the first several games as well.
There are really 2 players keeping Levine off the field in passing situations, and Mosley isn't one of them, because he's the signal caller. The 2 are:
Orr: Who has difficulty in coverage, despite being a decent pass rusher and some speed.
McClellan: Who is a regular moving piece in the 5-up, 1-down pass rush lineup Pees often fields (Jernigan, 2 OLBs, Mosely, Orr, McClellan). McClellan is a fish out of water in coverage and despite a recent sack, has no more ability to get to the QB than Levine (both need to use quickness and would have great difficulty winning a 1-on-1 battle). As an aside, McClellan lined up at DT from a 4-point stance on the 3rd and 22 play (Q4, 6:53) and was flagged for IH.
There are 2 ways to get Levine on: 1) Move Orr up to the LoS and remove McClellan 2) Remove Orr for Levine. Either way should give the Ravens more coverage options with little reduction in pass rush. The 2000 Ravens used method 2) to replace Jamie Sharper on 3rd down (with Corey Harris). The following year, Sharper became an integral part of the pass defense, so they used method 1), but still played a dime DB next to Ray Lewis.
