The map was made back when there were plenty of pros and newbs alike to play the game of archer friends. If you have a max health lumberill sitting there, you'd have to wait for 20 minutes while killing it because sometimes new players don't know how to leave when they lost or good players Alt-Tab at horrible times.
You can't make a separate space for lumbermill unless you put a hall there with it too, which would change the pace of the game because everyone would start with a 2h. If you isolate your mill you would have less choppers, or start off with too many choppers and take out the resource management part of the game out.
Peon defending is very different than a peon rush. It is the only way to defend a 1h if you are a 2h. That argument doesn't make sense, you cannot compare apples to oranges.
Edit: And there is a space for the mill, it's why the tree line is bent at a 45 degree angle. It's supposed to be naturally protected so that people don't send archers down there. But wood rapers like yourself (
) go through that tree line anyway.
