A large issue with this is the fact that certain armies of different strengths can only exists in certain time-frames, so even if you could perfectly calibrate

A large issue with this is the fact that certain armies of different strengths can only exists in certain time-frames, so even if you could perfectly calibrate for "this army combo is as strong as every other", the fact that one unlocks parts of these at different times makes this approach totally unrealistic. Since the unlocking of army combos is extremely rooted in economy, map layout/resources, power spikes of opponents ect.