Stats will never show what a defensive linemen does in the 3-4. Shaun Ellis didn't control the line of scrimmage the way Seymour did. Ellis did a good job, no doubt, but he is part of the run defense problem...not the biggest part, obviously, but a part of it.
Not saying that Ellis is as good as Seymour in the 3-4. But dont you think that kind of the reason that Ellis didnt dominate the line is because he was the only threat on the line? When Seymour had Warren, and Wilfork with him. When Warren didnt play against us the 2nd time, thats when we beat them. Though Seymour ended up coming out, but still we were winning when he did. Seymour is injury prone too, he played only 2 full seasons during his career. Atleast he is sort of injury prone.
Plus Seymour is more built for the 3-4, Ellis is a better pass rusher, but Seymour is better verse the run, he is bigger then Ellis. Ellis gained weight though, I heard he weighed in over 295 at the begginning of the season, Seymour is over 310. Man though, if I could take one person from the Pats defense it would be Seymour in a heart beat!