Heh … many, many years ago an article was published about how heavy are fantasy giants. Double the size keeping the proportions weight increases eightfold. Half the height with consistent proportions results in 1/8 the weight.
So half the weight would be something like 79.3% of the size.
I recall high school physics where we learned that a bone’s cross sectional area determined its strength. So the bone strength went up with the square. But the weight that it had to bear went up with 3rd power. So… the proportional man could only grow till his bones broke.
Many many dead zones on the planet. Areas that cannot recover quickly. Gotta be a limit to how much our planet can digest. Old adage ( that mankind seems to ignore ): Ya don’t shit where ya eat. The good news is, once humaity is erased from the planet, the Earth will begin to regroup; and in a few million years, a drop in the bucket in geologic time, the Earth will be all sparkly once again. So there’s that.