I’ve been reading about PIE and i’m confused. As I understand, it is assumed to be the language spoken by Europeans 6,000 years ago. No written record of the language has ever been found so the language has been reconstructed through seemingly arbitrary means. So, In all likeliness actual PIE sounded very different. What makes this language (as it exists today) useful? This is essentially a conlang that is too complicated to learn. What am I missing? Sorry if I’m coming off as negative. I find PIE both confusing and fascinating.
I think the big problem is that you seem to believe that the reconstruction of PIE is done according to whim: The reconstruction of proto-languages like PIE is done using what’s called the “comparative method” (that’s your magic word to look into) and is continually refined based on new evidence, taking into account the age of the evidence (i.e. Gothic, Sanskrit, Ancient Greek, Hittite, and Latin texts would be closer to PIE than modern languages) and the observed trends of how languages have tended to change over time since the invention of writing. So the reconstruction of PIE is very scientific in fact, and the reconstruction of laryngeals in PIE in like 1879 actually correctly predicted the location of ḫ in the descendant Hittite language, loooong before that language was deciphered in the 1920s. So if PIE is bogus we wouldn’t expect it to have any sort of predictive value, but it clearly does!
As for the use of PIE, or proto-languages in general… Well, they can help chart out human migration, they can tell us about the development and spread of technologies and ideas, they can tell us about what ancient societies were like, they can help us decipher undeciphered descendant languages, and things like that. And for learners of modern languages, historical linguistics like proto-language reconstruction can help explain why certain grammatical features in a language work the way they do. For instance, I’ve noticed that Russian verbs often end in strikingly similar ways to Latin ones, because they share a common ancestor.
A final thing: PIE was not spoken by “Europeans” 6,000 years ago. PIE was spoken by an unknown culture — the leading theory is the Yamnaya culture in what is now Ukraine and Russia — and then spread out across Europe and much of Asia in a series of migrations. Following these migrations, the communities of PIE speakers grew isolated from one another and had their common language gradually diverge into many different languages, which gradually diverged into new languages in turn. A notable thing is that when the Proto-Indo-Europeans migrated westward into the bulk of Europe, there were in fact already people there who spoke their own completely unrelated languages. Only one of those “paleo-European” languages has a surviving descendant today, that is Basque.