It's tough because the Titans offensive line has been a dumpster fire this year, so you're comparing apples and oranges. Lewis also has a pretty clear role as a receiver out of the backfield that Sony has not yet begun to match.
I'm not one of the people making that argument, I think Sony's been very promising overall, but I do think there's something to be said that's indicsted by Phillip Lindsay is averaging nearly 6 yards a carry as an undrafted free agent. My problem with the Sony pick was always that spending a 1st rounder on a running back is a highly questionable investment rather than Sony as a prospect (I'm still skeptical of the knee thing because Lombardi was the one reporting that and I think he's a hack), though I preferred Derrius Guice. It's just much easier to find a good or even great running back later in the draft or on the scrap heap (Lewis himself is proof) than it is for any other position and the Patriots could have drafted the likes of Darius Leonard, Harold Landry, Courtland Sutton, Dante Pettis, or Anthony Miller... and then found a running back like Guice, Kerryon Johnson, or one available later.