My point is more like the runaway arms race of intelligence is pretty tricky to figure out. Sure, one thing is clear - if it only happened inside one species, the selective pressure was inside the species: not adaptation to the environment (that would predict a world where we have 70 IQ chimp servants) but something inside the species, and given that it has to be a pressure, a do-or-not-reproduce kind of pretty tough stuff, and being nice and empathic with each other is not a pressure, it must be some kind of a competition. So far it is not a new idea, but a rehearsal of the most popular hypotheses.

Now, my point is simply you got a factor inside the hominid species, a factor X, which leads to the runaway arms race of intelligence, an Y. My point is, what if they are the same?

It is Occam and Solomonoff at work here. Usually we assume two variables, an unknown factor X launched a runaway arms race of intelligence, Y competition inside the human-hominid species.

So why not ponder the possibility that X = Y ? What if intelligent offspring killing / tying up mothers due to big heads led to males more intensely IQ-compete for the women who were not dead nor tied up with a child or three?