Attached is my rankings for my current season (2035). Firstly note that, due to my recruiting restrictions, my team is only an "A" OVR with a "B+" offense, so it's not like I'm playing w/ a 99/99/99 rated team.
My passing D is only ranked 54th (I'm usually closer to the top 20), but this is mainly due to teams trailing in the 2nd half all season and having to pass the ball) but still we're only allowing 213 passing YPG, which I think is pretty respectable.
I checked my schedule and we haven't allowed even 300 passing yards in a game this year, let alone close to 400+. Here are the passing yards we've allowed so far this year:
Pitt: 288
BGSU: 148
Oreg: 144
ND: 239
PSU: 105
Nebr: 293
Ind: 263
MSU: 228
EDIT:
I see that you had an issue w/ MSU's QB having 20 YPC. I also attached the QB stats for the 2 guys that passed for the most yards against me. They averaged 9.2 and 10.6 YPC against me. It's rare that my guys get beaten for big gains. I think this is mainly due to the solid zone defense that they play. It's very rare for my safeties to get beaten over the top (I'm usually in at least a cover 2). I hear people complain all the time about out routes and especially corner routes, but my guys cover both of those routes (and curls) very well most of the time.