Two important factors that are often neglected in discussions are the tradeoff between upgrades and the marginal cost to incorporate units.
Both are crucial from a civilization design perspective and relevant in-game situations.
For instance, choosing between two conflicting upgrade options like 2hs+drushina and champ+blast furnace requires weighing the cost-benefit ratio and contextual variables.
Similarly, mixing units like mamelukes and heavy camels can lead to better outcomes for little marginal cost.
The key is to strike a balance between going for the fully upgraded version and a combination of cheaper options that offer marginal gains.
Mixing units requires careful calculations, separate control groups, and practice, but overall it can be a useful tactic to reduce costs and smooth out transitions.
From a civ design perspective, overlooking the marginal cost can lead to unintended consequences and balance issues.