In truth,
I think that Legursky will line up better against the Packers D than he would against quite a few other teams. The main reason, is size vs. mobility. Legursky is bigger and not as mobile as Pouncey. Playing a 4-3 would hurt us more because Leg. would have to account for stunts and move quickly to pick up inside blitzes.
In the 3-4 schemes, Leg. has to worry about 2 things. 1. The NT. 2. Who's coming through the A gaps if the NT stunts. Leg. is strong. Strong enough, IMO. to limit Raji from taking over the game-or affecting play-calling any more than what would have been done with Pouncey.
Where missing Pouncey is going to hurt us, is 1. The run game. Pouncey is VERY often seen 15, 20, 30 yards up field throwing other blocks. Leg. doesn't have the speed. 2. As said before, calling the protections. However, with 2 weeks of preparation for 1 team, and the extra work he is putting in, I don't look for that to be as much of a problem either.
I just hope that the 1 or 2 mistakes he'll probably make will either be turned positive by Ben or Mendy, or will at worst end up being neutral.