Dan
You are absolutely correct. Fatigue is the real enemy and one that most airlines still treat rather glibly. One size does not fit all and every individual is different in how they handle fatigue.
No amount of technology is zombie-proof.
Simplicity is the best protection. I have average Vr numbers for average TOW's/sector times written on a laminated card in my wallet. It is the first thing I look at when I strap in. If the deus ex-machinus gives me a number that is 5kts away from this it is time to re-check everything.
Computers are fine but commonsense is the only thing that provides adequate insurance.