dactylic hexameter fits badly into the Ancient Greek language and thus is probably a loan from those mysterious Πελασγοί from the Minoan culture.
I think that’s a somewhat outdated view.
It’s true that it’s difficult to compose Greek verse in the dactylic hexameter (iambics are closer to the rhythm of Greek speech, and much easier). However, archaic Greek hexameters–particularly the Homeric poems–were composed to a large extent by stringing together fixed expressions (“formulas”) that fit specific metrical slots. A virtuoso aeidos would have had a huge repertory of these formulas in his head, and he would also have the ability to compose new material fitting hexameter metrical patterns on the spot, based on his training and experience. And even ordinary Greeks immersed in a hexameter culture would have some ability to compose hexameters on the spot, though not necessarily elegant ones. The crude 6th and 5th century Delphic oracular responses are a case in point.
As for the origins of the hexameter, it’s all speculation. In the 1920s, Meillet showed how Aeolic meters (such as glyconics) resemble to an uncanny degree the metrical patterns found in the Rg Veda, suggesting that the resemblances point to a common Proto-Indo-European origin for these meters. Since then, others have shown that meters found in Slavic, Celtic and perhaps other Indo-European language families might be traced to a similar origin. But these meters are all isosyllabic–each verse has the same number of syllables, and substitution of two short syllables for one long one isn’t allowed. From this, Meillet concluded that the hexameter, which is definitely not isosyllabic, did not trace its origins to Proto-Indo-European meters, but instead must have been adapted from pre-Greek, “Pelasgian”, poetry. (“Pelasgian” is the term the ancient Greeks used for pre-Greek populations, but there’s no evidence that these populations, scattered around Greece in the archaic and classical periods, spoke the same language or had any ethnic affinities with one another. It’s a term that is to be avoided.)
In more recent years, other scholars, including M.L. West, have questioned Meillet’s conclusion on this point. It’s possible to see the hexameter as having arisen as a conflation of various Aeolic-type verse-forms, with at some point the allowance of the substitution of two shorts for a long, or vice versa, perhaps due to changes in Greek phonology such as contractions of two short vowels to form a single long vowel–without the need to resort to a hypothetical “Pelagian” origin. Again, this is all speculation, of course, but as far as I’m concerned, I think that the origin of the hexameter can probably be most plausibly explained this way (even if the details necessarily remain obscure) rather than by resorting to a “Pelasgian” hypotheses, which can’t be proven or disproven.
Incidentally, I don’t mean to cast aspersions on Meillet. He was a towering figure in Indo-European, as well as ancient Greek, studies. Among other achievements, he showed that Armenian was an Indo-European language with certain affinities to Greek. It was he who suggested to his student Milman Parry the idea of studying oral composition in Bosnia, where there were still living exponents of the tradition. This led to a complete revolution in understanding the Homeric poems, the consequences of which are still being debated and worked out to this day.