I sympathize, and I really don't know how PD happens. AJ Hawk starts at, I believe, an 85 OVR - two seasons past, and I believe he's up to an 87, and that includes a season where he had close to twenty sacks. Go figure.
I've got a pretty dominant defense built - I hold teams scoreless more often than not - but development isn't as rapid as I would expect, especially on the defensive side. QBs develop rapidly (Green Bay coaches see to that), but others seem to lag.