It depends on what you are considering. If 1/20 people of a population were 100% Neanderthal, and the rest 0% Neanderthal, over millenia, and assuming random m

It depends on what you are considering. If 1/20 people of a population were 100% Neanderthal, and the rest 0% Neanderthal, over millenia, and assuming random mixing, the whole population would tend towards what it is today. So we are potentially heirs of a population where Neanderthals mixed with non-Neanderthals in a (very) broadly similar ratio as Europeans versus non-Europeans in the US today. I only intend this to illustrate that 5% is not as trivial a number as people often imply, and that it potentially derives from a population of Neanderthals and non-Neanderthals mixing in quite a "modern" fashion. I would add to this that one interesting fact concerning human-neanderthal genetics is the absence of Neanderthal mitochondria in modern humans. This may mean that Neanderthal women couldn't bear human-Neanderthal offspring, and if they could have, the proportion of Neanderthal DNA in modern humans might have been twice as high as it currently is.