wow, this topic sure is jumping around!
MMmmmmm I am not sure what to address first. I think at the moment technology is advancing too fast for scientists to successfully use it properly, either that or they are incorrect in their interpretations of the data presented to them [you only have to look at the mDNA testing done and the differing interpretations]. There is a poster at my university that says "If we are to understand the present we must first understand the past".
It is my understanding that H. erectus was the first species to migrate out of Africa, that they managed to superceed existing hominid species and evolve (?). Anyway - I haven't done much study on Neandertals. But I do know that many features in H. erectus can still be seen in African tribes today, that 'archaic' modern human traits can be seen in modern Asian populations also. Perhaps, even though Neandertals showed signs of progressing forward they were too slow (?), were bred out of existance(?) - who knows.
Keep safe
Bella