A quick clarification — Joe Brady is the Bills' new head coach (promoted from OC after Sean McDermott was fired), not their OC. The defense is his in the head-coach sense, but it's Jim Leonhard's scheme to run.
Here's the outlook on whether they'll improve:
Yes — the defense looks set to take a real step forward. Here's why:
Scheme change from passive to aggressive. Leonhard is flipping the Bills from McDermott's bend-don't-break style to a 3-4 attack scheme with heavy blitz packages. It's a completely different mentality — "4-quarter attack" is how the wiki describes it (from the Jim Leonhard page).
Leonhard's pedigree. He came from Denver, where he was pass game coordinator for one of the league's best defenses (the Broncos that won Super Bowl LIX). He was ranked among the top-10 new coordinators for 2026.
Six defensive draft picks. The Bills used 6 of 10 picks on defense — headlined by DT T.J. Sanders and CB Davison Igbinosun in the second round, plus safety Jalon Kilgore in the 5th. They also added Bradley Chubb in free agency.
Breakout candidates identified. Maxwell Hairston (CB) and Cole Bishop (S) are both expected to thrive in Leonhard's aggressive scheme (from the Jim Leonhard page).
The fantasy angle: More blitzing = more sacks and turnovers, which should make the Bills DST a strong streaming/roster option. The only risk is aggressive schemes can give up big plays to elite QBs — which matters given they face Mahomes (Thanksgiving) and Love (Week 14 SNF). But the new Highmark Stadium's crowd-noise tech should also help rattle opposing offenses at home.
Bottom line: Between Leonhard's scheme, the draft haul, and the Chubb addition, this defense should be noticeably more disruptive in 2026 than the passive McDermott-era units.