What was a proportion of children born with one parent a modern human and one parent a Neanderthal some 40,000 years ago?

We know that current humans have around 2% of Neanderthal genes (except for Africans). Neanderthals became extinct some 40,000 years ago. I would like to discuss two assertions:

1.) Some 40,000 years ago humans already had 2% of the Neanderthal genome.

If not, then through many and many generations up to now this percentage would naturally decline to a very small amount. But if (all) humans already had 2% of Nenaderthal genes 40,000 years ago, than even when human population grew to 7 billion, this percentage would not change.

2.) Now, if we assume that Ad 1) is true, then it means that 1 in 25 children that grew to adulthood (capable of breeding) was an offspring of a human and a Neanderthal. If only mixed children were born, than the resulting population would have 50 % of Neanderthal genes. Since it should be only 2%, then the proportion is 1:25.

What do you think about it?

It would be interesting to perform simulations on human-Neanderthal breeding, since we know the final state (2%). Parameters such as the number of children of both races or the ratio of inbreeding could be considered and modeled so that the final result is in an agreement with the current state.