I think Sashi's biggest problem was retaining talent. He was also too quick to cut or trade vets before the young guys had a chance to even prove themselves on the field. He was too willing to open up starting spots for draft picks without them earning it. It's something that couldn't have worked long term.
Farmer is definitely high on the list of bad GMs but the Mangini/Kokinis was real bad too. Mangini ran the draft we got Alex Mack and everyone else was a bust. He has admitted he used a draft guide from a independent scout to make his picks. There were alot of rumors that Kokinis was just a GM in name and Mangini was always running the show.