Better question, if there are 100 visas allowed, and 80 experts needed for software, and 50 experts needed for bio, then how do you compare software experts vs bio experts? What metric do you use to justify someone is more of an expert overall? It is apples and oranges.
Arguably, the most effective justification is that experts in X are compensated higher, therefore they must extract more value for the US economy, than experts in Y. A simple sort on minimum-guaranteed-salary seems best.
However, this stops being the case if we have no cap. But a limitless H1B systems is not a likely reality.