Tree groups exist to reduce the draw calls. It's why they are part of the game. This is what happens when you break all tree groups on Seton's Clutch at the start of the game:
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Note the statistics on the left. Meanwhile I have a 7950x3d with a Radeon 7800xt. And with tree groups:
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edit: breaking all tree groups also casually pushes the initial RAM usage from 470mb (with tree groups) to 780mb (no tree groups) at the start of the game 🙂 . That increase is more than 15% of the budget that FAF has available because it is a 32bit application