You've nailed the biggest reason for the 1-3 record, IMO, coupled with the lack of takeaways. The D can't get off the field, and it's killing them.
Teams have figured out the Bills blitzing schemes, apparently, and they're not getting enough pressure from the DEs (to be fair, this may be by design the last two weeks - to contain a running QB rather than doing a hard rush from the outside).
Sigh....