Beane and McDermott asked Epenesa to "slim down" (just google it, you'll see plenty of references to it) after Beane talked about loving his measurables on draft night.
This scheme and philosophy are the problem.
Eagles attack and prize big, physical linemen on both sides of the ball. On D we seem to want quick smaller guys, and the scheme is to sit back, keep the game in front of you, come up to make tackles and don't give up anything big.
Wait for the QB to make a mistake, or the OL to hold, or someone to drop a pass. and it works a lot, until you play elite teams.
I want my 350 lb DT this year in the draft! 340 is fine too, because he can put the work in at the cafeteria to get where he needs to be.