I think counters would be an interesting thing to study as a linguist. Similar to I think it would be cool to study how languages define if a word is plural.
I haven't come across any such study but I would love to read it if it exists. In the meantime, I highly recommend The Story of Human Language as well as The Adventure of English lectures. You can find both on Audible, just make a free trial like everyone else.
As a linguist, it's hard enough to get your peers to study not-European, well, anything.*
It isn't all their fault. Currently our lack of information in non western languages made available in our languages is so small that it would take a fair amount more work (and probably a fair amount of East Asian linguists who are native speakers!)
*Currently linguistics remains heavily studied primarily in Western spheres, though there have been happy growths in areas like India and China, but we need more.
There is a specific counter for "long things" ?! Why would someone make a language so complicated...
It always looks more complicated in a language you're learning, but only because your own language is second nature to you. Think BLADES of grass, STRANDS of hair, SLICES of pizza/pie/cake (but not slices of, say, lasagna). The more you think of it as difficult or complicated, the more difficult and complicated you'll find it to be. Try (though it can be tough when it gets a bit confusing) to find it fun and interesting! A good challenge.
And there are many other counters, for example: people, bottles, houses, animals...
I have always found that people who insist certain languages are more complicated have simply said so after finding one of the only parts of a language that are particularly inaccessible to them compared to their own, i.e. "English, French, German, etc don't have counters so this is confusing and strange!"
Which, I mean yeah, counters are difficult for Romance and Germanic languages (and several others), but the rest of the language is about par for the course for language learning.
While it is true that certain languages are "easier" for certain people from certain native languages and the reverse is also true — that some native languages make other languages "harder" (a bit of a dubious claim to make so far and wide, but that's a different discussion altogether...) all languages take intense dedication and constant inward motivation and daily attendance.
I promise you if you have that, counters are no sweat
Any reason that the counter receives the subject particle? Is it because the NOUN-NUM-COUNTER segment is treated as a single unit?
Exactly. Just like how in English, in the sentence "I have one pencil", 'one pencil' is the noun of the sentence. English just forms it more like NUM-NOUN, and there is no counter word.