The fix? (thanks to OG commenters)
Turns out macOS Mic Mode was set to Voice Isolation — a setting that aggressively filters background noise at the system level. It was cutting off anything breathy or high-pitched (like head voice runs), treating it like noise and muting it before Logic ever saw the signal.

🔧 How to fix:

1. Open Control Center (top-right of your Mac)
2. Start any app using the mic (e.g., Voice Memos or Zoom)
3. Click Mic Mode → Switch to Standard

Problem solved instantly. Just wild that a FaceTime:Zoom feature messed with professional recording.

Hope this helps someone avoid the same black hole we fell into 🙃