>The human element is what makes these calculations non-deterministic.

I agree with you. But hand (and position) value concept uses such concepts as expected value and standard deviation.

The concept of EV (expected value) was designed with intention/aim to cope with future uncertainty. This means that if there is an uncertainty, for example as in our case (poker), EV is an ideal tool to use it in this situation.
We do not know other players’ cards and strategies, but we do can estimate their probability distributions. From these probability distributions we can estimate EVs and other statistical parameters, for example variances, standard deviations, etc.