Here's how I understand it.

First, there's a famous Tyutchev poem from 1866 which is known by pretty much every Russian

Russia cannot be understood with the mind alone,
No ordinary yardstick can span her greatness:
She stands alone, unique –
In Russia, one can only believe.

(This is essentially word-by-word translation.)

So Tyutchev claims that Russia is so unique it cannot be analyzed. I think "The Russian Field ..." represents an analysis of Russia's uniqueness through enumeration of paradoxical archetypes which Russian culture holds, which makes Russian history/existence itself paradoxical, and thus uniquely fucked up.

The song mentions elements of the following archetypes/themes:

1. greater aspirations - God, etc.
2. lust
3. brutality, desire for destruction
4. desire for greatness/domination

Of course, they are present in every human culture. However, song combines them in a paradoxical way. It's as if different layers which are supposed to be distinct are brutally mixed. And the resultant mix is not pretty.

How did it happen? The song does not answer directly, but we can figure from the history: Russia's societal development got delayed, particularly, in XIX century. It was still an agrarian country with deeply religious population, but at the same time it got aspirations to play a global role.

So e.g. suppose you're a peasant. In Church you've heard there's God, God set Tsar to rule Russia, you're supposed to love your Tsar or you're a bad man. Then you're recruited into an army and go to war and shoot at other people. Why? I guess nobody would explain, but presumably God wants and because you love Tsar you have to do it.

The song might reference this retarded societal development in line "On the patriarchal landfill of obsolete concepts", "patriarchal" referencing Orthodox Christianity and Tsar-father as a head of everything.

Thus we have a mixture of 'greater aspirations' layer with 'brutality of war', e.g. in song this paradoxical mixture is referenced e.g. in "Laws of etiquette for mortars" line. There the word for "etiquette" is actually more vague term which can be found in Bible teachings, so it hints of mixture of ethical teachings with howitzers.

But then Russia went from insanity of Orthodox monarchism straight into the insanity of communism, famous for its double-think, etc. So Russia's collective unconscious never had a chance to clean up and unmix different layers, but got even more confused.

As a result, greater aspirations did not become a guidance, but merely a veneer hiding the brutality.

You can see this happening now - Putin talks about God, unity, saving brothers, etc. But people are brutally killed and raped. And for Russians it makes sense, it is a part of an archetype - God. Greater good. Howitzers go BOOM. They are used to this.

I asked my friend "So you want to save Russian-speaking people in Mariupol from "nazis". Why are you bombing the city?!" He replied: "Of course, it makes sense - that's how liberate a city from nazis, you gotta bomb it, that's how they did it in WWII". For him, it makes sense, he saw that in movies.

So anyway, I don't think it's nihilism. Letov describes some dark fucked-up archetypes under a veneer of Russian culture, but he doesn't make predictions about the future here (aside from a possibility of these archetypes materializing - which we see, unfortunately).