4-3 vs 3-4, the main personnel issue here is the OLBs.
If we stick with 3-4 we have to find two new defensive ends.
What's easier, finding two playmaking 1-gap DEs, or finding two decent OLBs who can cover?
You can find starting OLBs in the middle rounds of the draft and in free agency EVERY YEAR. It's hard to find premium DL talent in comparison.
I have no issues switching to a 4-3. You stick Powe and Poe in the midde, Hali and Houston on the ends and roll with it.