To be fair, if I recall it's only in the last 15-20 years that the Altaic theory seems to have gone from 'speculative' to 'not at all likely.' Those of us who studied this stuff 20 years ago could easily spout off this 'might-be fact' if we didn't bother to verify first.
I guess at this point similarities between the two languages are assumed to be a result of regional influence?
Many mainstream linguists have been against the hypothesis since the 1950s, but there are still plenty of linguists who contend that the Turkic, Tungusic and Mongolian families form a family; a smaller number have arguments in support of the stronger claim that the Koreanic, Ainu and Japanese–Ryukyuan languages are connected as well. See eg: [0] Vovin set out to demonstrate that the latter, stronger claim was true and ended up writing this: [1]
Arguably, the biggest blow struck to the hypothesis in the last 15-20 years came when Vovin, previously a supporter of the hypothesis, wrote "The end of the Altaic controversy"[2]. Among the more notable arguments in it is that the non-traditional methods[3] used to argue that Altaic is a family are rejected by traditional comparative linguistics because they overweight lexical comparisons.
This was a rather prescient point, as some of the methods that have developed since then that have been used to argue in favor of the Altaic hypothesis suffer from this problem quite badly; this is perhaps especially true of the Bayesian phylogenetic inference, sometimes called Bayesian phylolinguistics when applied to historical linguistics. With this technique, used in eg [0], it is pretty hard to argue that this method wouldn't overweight cognates and loan words gained through contact unless you specifically control for that, which will cause you to end up erroneously marking sprachbunds as true families.
See [4] for another usage of the technique, this time to support the Dravidian family, which is already very very well support by traditional comparative methods.
All of this ultimately points to what I think is the real answer to the issue; outside of some arguments about archaeology that I don't have enough background to evaluate [5], most of the shared bits (shared pronouns, lexical stuff) between the languages here exist because of contact.
The languages here, if they belong grouped at all, should be grouped as a sprachbund, not as a family. The possibility that there is a true family with "micro-Altaic" is small, but I think it is still a much greater possibility than the "strong" hypothesis (w/ Japanese, Korean, etc). This paper [6] has a very cool approach to evaluating the weaker form of the hypothesis that I think most HN readers would find interesting.
So to answer your question, yes, I believe your assessment is correct, and mainstream historical linguistics does as well. But I wouldn't go so far as to say there are any nails in the Altaic hypothesis' coffin just yet.
For an amateur's blog post in 2009 to call Altaic theory utter horseshit would been rather hubristic to begin with, and moreover, not even the point. The Altaic hypotheses were higher-profile proposals that happened to include common origin for Japanese and Korean. Even dismissing the former, the latter is not exactly out of consideration.
And, as the post points out, the whole line of argument is a curiosity that has little concrete bearing on the fact that the two are very similar from a learner's perspective.
The Altaic theory isn't necessary to postulate a connection between Japanese and Korean. It's known that genetically the Japanese population was seeded by Korean settlers which largely displaced the native Ainu populations. Japanese is likely a descendent of the language spoken by these colonists from the Korean peninsula.
The two languages are very divergent, and the usual mechanisms for classifying languages are difficult to apply because the dominant Chinese influence came to each separately after they diverged.
> It's known that genetically the Japanese population was seeded by Korean settlers which largely displaced the native Ainu populations
It's even more complicated than that. In addition to the Ainu there were the Jomon people, a non-agricultural but nonetheless settled society who are believed to be the first people in the world to use pottery - which is surprising for a non-agricultural people.
They might in turn have been an offshoot of the first migration of modern humans out of Africa along the south coast of Asia, whose haplotypes [1] occur today at some of the highest frequences in Japan and as far north as Mongolia and as far south as Australia. Some sub-branches spread west all the way to the edge of Europe.
I think the latest thinking is that all people of Japan to varying degrees are descended from the Jomon people along with other populations migrating from mainland Asia over millennia.
This pattern - early hunter gatherer populations forming the substratum that later mixed with larger migrations of agricultural populations - is not unique to Japan.
It's quite similar to what you find in the paleogenetics and history of most regions of the world, including Europe and South Asia.
My understanding of more recent European population studies is that the genetic signature of the pre-agrarian hunter gatherers is actually quite low. In general they were displaced rather than merged. Or their numbers were so low and diffuse that their contribution was little. Which makes sense when you consider population densities possible/typical in a hunter gatherer vs agrarian lifestyles.
We're back to population migration / replacement theories being ascendant rather than the situation 30 years ago when cultural diffusion theories were preferred.
10% of the average Briton's ancestry (for those without recently migrated ancestors) is attributable to West European Mesolithic hunter gathers. That's a pretty significant chunk, suggesting both migration and mixture happened, and not diffusion or replacement.
"When we look at genetic variation in modern British people today, we find that – for those who do not have a recent history of migration – around 10% of their ancestry can be attributed to the ancient European population to which Cheddar Man belonged. This group is referred to as the western European Mesolithic hunter-gatherers. However, this ancestry does not relate specifically to Cheddar Man or the Mesolithic population of Britain. Well after Cheddar Man’s death, two large-scale prehistoric migrations into Britain produced significant population turnovers13. Both of these migrations into Britain represented westward extensions of population movements across Europe10-12. In both cases, these migrating populations intermixed with local people who carried western European Mesolithic hunter-gatherer ancestry, as they moved across Europe. When these populations arrived in Britain they already had some hunter-gatherer ancestry derived from this mixing with local populations. Therefore the majority of western European Mesolithic hunter-gatherers ancestry that we see in modern British people probably originates from populations who lived all over Europe during the Mesolithic, which was carried into Britain by these later migrations."
While a relationship between Japan and certain lost languages of the Korean peninsula is agreed upon by nearly all scholars, that still doesn’t necessarily mean that Japanese and Korean are related. One recent school of thought, for example, is that pre-Proto-Japanese entered the Korean peninsula from mainland China (Shandong province) while Korean came down from the north, so they would not be genetically related in spite of being neighbours.
I guess at this point similarities between the two languages are assumed to be a result of regional influence?