All good statisticians are careful to point out the they cannot prove a negative. So reputable studies about clutch hitting can only say "we can't find it." For me, that's good enough to say it should not be modeled in a game.
It's much like catcher defense. The Bill James's of the world worked hard to see what kind of impact catchers had on defense for many years, and basically said "we can't find any--or at least not any that really differentiate between catchers." It took advanced work on framing to really find anything. Time moves on. If clutch hitting actually exists, there will be a way to quantify it.
Until then, argue all you want.
