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I agree with Er@ser.
You also need to consider the player's skill level. I'm sure that 80% of players, after receiving 8 free heroes at the start, won't know what to do with them.
And not everyone will be able to effectively fight battles with an army from the first week.
So, the question is - why spend money on something you don't know how to use?
Before spending money on an army and heroes, you need to learn how to accurately assess the consequences of battles, build efficient production chains, clearly plan hero movements, and have certain tactical skills. And until that happens, it's more effective to invest in income. For 80% of players, the right first move is a prefecture (1000 income).
I know what to do with the 8 (free) heroes; I know that resources are plentiful, and I can build a production chain for my main hero, and I have a pretty clear idea of what I want to do, and I usually don't wander aimlessly around the map. But I still build a prefecture (depending on the situation) as my first or second move because I don't know if I'll find money on the map or not, so at least I'll have some kind of buffer for development:D