He missed seeing wide open check downs more times than I can count, and that's not about arm strength (Pyne actually has a pretty good arm) it's about him not seeing things well.
If I was to list just one thing Hartman seems vastly superior at over Pyne, it would be field vision. It's just one area, but it's a big one...so many of our punts should have been easy conversions if Pyne just took the check downs.