I think the engine reacts too. It generates the match before it starts, and every time someone makes a change, the rest of the game is being recalculating. A red nickname said once, that in some cases the engine simulates a match in the background, and it happens almost instantly.
We have only three levers on the game: formation, orders and subs. I'd like to see an experiments like this, but with each of those tested independently, not together.