Just to preface, I'm a scientist: micro- and molecular biology. I'm not saying to take what I say as gospel, just giving context that I might know things. Sometimes.
Outbreeding depression has more possible implications than fertility decrease and infant mortality increase, entirely dependent on the heritable traits responsible for the depression effects. While the probability of persistent outbreeding depression seen in subsequent generationa would be lower due to traits subject to higher selective pressure, like increases in early infant mortality, the overall probability of outbreeding depression itself isn't influenced post facto by its results, just its persistence.
Given we don't know the original extent of neanderthal/human interbreeding, what we're seeing now COULD be the "much lower percentage" you mention and still could come from multiple events. In fact, if these crosses resulted in stronger depression effects, I'd argue a greater number of crossings would be one factor behind the persistence of some genes today.
I couldn't agree more. I initially went to a small community college. I took o chem twice because my first professor was so awful that the entire class would have bombed if he didn't curve the entire course so hard that we all got Bs or above.
When I retook it at a state university, I learned our confusion was due to him having no goddamn idea what he was talking about. His lectures didn't match the textbook, which is why we were getting marked off for what often turned out to be actually correct answers on the tests he made.