I'm not commenting on your suggestion, however I would like to mention one thing, I think, in warfare mechanics of this game, the definition "WEAK" and "STRONG" units in your example is not relevant.
like if you have hoplites and steam giants, in ground battles, hoplites come before steam giants, no matter which upgrade has the hoplite, or fire ships before steam rams in sea battles no matter how high upgraded fire ships are.
Whatever combination of units/ships are engaged in a battle, there is predefined order that forces them to take turn in fighting, it is up to participant to decide what kind of units to send in or pull out of the battlefield.