Most of the alloying and cooling was developed without even looking at what you call the microstructure. Current-generation optical microscopes are easily capable of observing individual surface crystals under elastic and inelastic deformation.

The effects of a given heat treatment on a given object is fairly simple to measure, but to predict the effect of an untested combination requires deeper understanding. Trial and error can create isolated useful developments, but understanding the next level allows accurate prediction of interesting developments. For example, the effects of alloying agents in iron remain experimentally determined, rather than predicted.