Infra is lost due to combat yes but that is not the point of scorched earth. The point is to avoid combat while luring the enemy inside the territory, and leaving them no means to sustain themselves logistically. Tank duels in a city damage the building, this is simulated yes. Blowing up railways while avoiding combat altogether isn't.
Destroying factories is fine but it is not a tactical move. It doesn't help defeat the army that is passing through that area, while the option to blow infrastructure does.
If the infrastructure is gone, then does it matter if you pressed a scorched earth button or not?
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