MMH5.5 - Heroes of Might and Magic 5.5

I agree, but in WGE, you have a predefined timeframe for meeting with your opponent (~6 weeks), which means the army size is predefined on both ends.

No, ~2-3, maximum 4 weeks. But this is "on paper," the target game time.
These numbers might shock you, but in reality, on some maps in Heroes 3 (like the Diamond template), you can develop and build a lot of cities with armies in that time. And play exactly the same strategy as you, but without the tedious wait of many months of gradually clearing out neutrals.

4-6 weeks is how players usually play in Tournament Edition.

Ok. I think I have an idea of what we can do. We can set "Wind dancer" base defense to 0 and set agility to +2 or +3? Not sure if it won't become stronger than its counterpart in practice, but it will definitely add tactical variation.

Yes, but it would be even more logical to reduce the damage rather than the survivability. Especially since their damage is "somehow" higher than that of the competitor (for the same target).