As far as I know, the adaptive radiation theory is now held as correct for hominids just as it is for every other group of species. The "classical" teleological viewpoint doesn't hold up to scrutiny for the reasons you cited.
Not every period of evolution in a taxonomic branch is going to involve adaptive radiations. Although early human evolution is generally thought to have involved an adaptive radiation, by the time we get to 2mya a lot of the literature was assuming only 2-4 species existed over the next 2 million years.
I don't doubt the integrity of the scientists who were involved with the earlier literature, but in hindsight it looks an awful lot like a teleological bias.