The defense is not a new system, it is a continuation of last year's system. There were a lot of defensive players in FA and we signed Takitaki and Hawkins, no-one else of significance. This year's players are the same as last year (not meh since they finished Top 10 in 2023), and the Pats had a golden opportunity to sign more defensive players, i.e. Gilmore, Simmons, Wilkins, and others. So 1. it is not a new defensive system, 2. it is a continuation of last year's defense as evidenced in game #1, 3. the players are the same and there was a lot of opportunity to sign All Pro defensive players in FA, and 4. the coaching is Mayo and his hand picked defensive coordinator.
There is no excuse for a drop in the defense. It almost sounds like you are making excuses. The only reason for any drop is that Wolf did not sign defensive FAs and the defensive coaching sucks.