Here is what really happend several 10000's years ago, based on new research and some speculation:::
1. Focus on the 2 major hominoids groups left on Earth at that time.
2. Both 2legged humans originated in N.Africa ( NThal & HSap)
3. Forget the "Savanna" and "Tree climbing" Theory in regard Upright walking.
4. The modern Human is Aquatic based, it developed its upright skill by walking/fishing etc. in shallow rivers, lakes, swamps, Water is the only element that forces you to be upright, not tall grass or trees. The special H2O gravity makes it easy to stand up. Today 44 percent of the worlds population lives within 80 mls of water. The beeing Hairless & having a fat layer under the skin is also a cause of living in water.
5. The NT got out of Africa early, due to higher curiosity/aggression/fearless or was forced out. The HS followed later.
6. The NT & HS are able to interbreed, DNA is compatible.
7. Mosts skeletons were discovered in western and central Europe, general spread is assumed Eurasia.
8. The NT developed red/light Hair trades, due to many generations of Snow/cloud etc. conditions in Europe.
Todays connection::
9. The "ideal" fine balance of ~97.5% HS and 2.5% NT, mix of DNA was reached. This fine balance (aggression/fight/war vs intelligent life sustainability) created the rapid progress in the modern world visible today. Nearly 100% of all migration occurs still today, from ...to...you figure it out!!
10. If you know a RedHead, you can feel their fierce Nthal genes in their bones.
5. The NT got out of Africa early, due to higher curiosity/aggression/fearless or was forced out. The HS followed later.
...
9. The "ideal" fine balance of ~97.5% HS and 2.5% NT, mix of DNA was reached. This fine balance (aggression/fight/war vs intelligent life sustainability) created the rapid progress in the modern world visible today. Nearly 100% of all migration occurs still today, from ...to...you figure it out!!
10. If you know a RedHead, you can feel their fierce Nthal genes in their bones. I think most of what you said is very plausible. Where I disagree is the assumption that the aggressiveness comes from the NT side, rather than the more-recently-out-of-Africa HS side.
Consider the distribution of aggressiveness between African and non-African peoples. Also consider the distribution of intelligence. Could it be possible that the NT were exterminated by the African HS, not because they were less intelligent, but because they were less savage?
Survival in the cold North requires a higher level of cooperation and mutual support among people.