Faults:
1) Values 3 point shots 1.5x more than 2 point shots, while the immediate results justifies this stance, things like long rebounds, additional possessions, and fast break opportunities from the opposition is not taken into account. That said, Duncan still came up on top, which really is shocking.
2) Missed FTs do not lead to opposition possession half the time. A missed FT also rarely leads to fast break opportunities.
3) Your "formula" clearly favours players who shoots more as it is biased towards FT shooting (more shots generally leads to more FTs)