Def this. Here's a good discussion of these scheme issues.
I think our defensive struggles came down to, in order of importance:
1) Washington's offense is really good and Penix had the best game of his career; hats off to them.
2) Many of our DBs are poor in coverage, in terms of both raw talent and development
3) PK has a tendency to dial up defenses against good passing offenses that sometimes seem destined to lose even before the ball is snapped (see the video above).
On 2, some development issues that we have seen throughout the year are:
a) our guys do not play the ball well in the air. Even when they are in good position and are not burned, they never turn for the ball.
b) when they play up in man, they rarely if ever get good contact on the WRs to knock them off their routes and disrupt timing
c) our safeties take bad angles and make poor reads
On 3, I have a theory that Sark and PK's vision of the defense may not be completely aligned. During the season, Sark made comments at PCs that we needed to be more aggressive defensively. I've noticed we have played a lot more press man at the snap than we used to (during his Sugar Bowl availability, PK indicated some recent changes in pass defense had been made). We are not very good at it. Related to the video above, I think some of PK's blitz packages may be tied more to his legacy softer zoner coverages on the back end. This is just a theory though. If you listen to his PC, PK very much prefers a "make them drive the whole field" approach, but later in the season we played with much more aggressive alignments. Penix made us pay for this.