This would pose significant problems, for several reasons :
- Some games don't gave the country selection option, or some players (like me) like to select randomly and roll with the country they get, for the sake of change. You would be put at an automatic disadvantage in a case where, say, your infantry was weaker and your neighbor's tanks stronger, yet you get a country that consists mostly of plains. That's a guaranteed defeat.
- Differentiating the balancing of each unit according to nation, as you suggest, would force the devs to carefully reconsider and remodel every province on each map, to ensure each country has at least a few terrains where their troops do well. However, not only is that unrealistic, as irl countries do not necessarily have every type of terrain dependent on their geography, but this would also present a huge amount of work, all just for a change that is not only unsubstantial but would also upset 99 % of players.
