I remember learning about this in grad school 20 years ago (so this isn't exactly a new theory), what I remember is that the modern human "package" has a lot of interlocking parts.
There's the sight advantage from the upright posture, along with the ability to use our hands since we aren't running with them (for spears, gourds of water, etc.), a brain powerful enough to engage in 2nd-order thinking ("the gazelle will want to catch back up with his herd", etc.), less sun exposure so better heat endurance, an efficient jogging gait (humans have beaten horses at marathons[1]), and probably most importantly social organization and comms that allow coordinated pack hunting (this may even get to why small irises and white sclera in our eyes were selected for).