"and why modern chimps have seemingly gotten the short end of the stick evolutionarily.. and why they still exist if they are a past form of us."

The human is only related to the chimpazee. Chimapzees and humans changed alot with the time. Do you know that medieval humans were smaler than people nowadays?
Anyway the chimpazees brain is growing much slower than the human brain. As far as I know the octopos brain is growing the fastest, what would mean that the new human like kind would be a squids kind if it´s going on like now.
Why should the parent kind die if they produce a new kind??? If parents get a child with three arms they won´t die. But the idea is funny. "Ugh! We got a child with three arms! I can´t believe!!! *DIE <--- all humans without 3 arms*"

You know how many kind of insects, mammals, reptiles, bacterias, plants and everything else we have today? It´s like a root of a tree, the deeper you go the more little roots you will find. If you come to a point where the most minerals are, you will find the most little roots. If you come to a point, where the ground has no water and minerals, you won´t find many roots. And every root, has it´s parent root, but still no root is like the other.