Maybe this speaks of the weaknesses of abstract art when used for this. No one thinks of the Lincoln Memorial or Mount Rushmore or Taj Mahal or Arc de Triumph like this. In some sense, their memorial status comes out in the form itself. This is not the case with abstract art like the spomeniks.
Despite not knowing the details, you knew it was designed to revere or commemorate something even if you did not know the details.
I think the only monuments that are actually obvious are literal selections like statues, or Lincoln Memorial which is labeled in large capital letters exactly what is commemorated and why.
Otherwise all I can tell is “this building is special because its purpose is not easily apparent (and people don’t seem to fit inside it?)”
So now what? You origintally made the point to try to distingish between the power of representative art vs abstract art (although I'm struggling to understand what is more representative about the Taj Mahal and the Arc de Triomphe than these also).
Otoh it is quite evident to me that Spomenik monuments are there to commemorate something or they would be very different
Secondly I would say the fact that they provoke thought about what they represent (rather than say Mount Rushmore in particular which is a profoundly superficial public monument) is precisely part of the value of abstract art. The Lincoln Memorial says Lincoln was a great man. OK cool. Anyone who has studied American history knows that.
Does the fact that the French tomb of the unknown soldier from World War I was created beneath it change the meaning of the arch?
It seems to me it’s a pretty complex, abstract object whose story isn’t easily reduced to a simple meme either.
Interwar abstract art such as cubism had twisted and distorted figures, some was a reaction to the twisted and broken bodies of the veterans of WW1. Hitler hated that style of art because he saw it as disparaging veterans, war-glorifier as he was.
It would make sense that a ‘progressive’ regime would want to break with traditionalism and create its own novel style of monument. You see this trend in a lot of postwar aesthetic movements, like the failed housing projects of modernism. They don’t glorify anything; they exist imposingly and have a strong bias to function. Yet this itself is dehumanizing in its own way.
Tl;dr: traditional aesthetics glorify the nation and the state, including its human flaws. Abstract art tends to dehumanize itself as a way to avoid these flaws, especially in the wake of major human catastrophes.
The Soviet and Fascist styles of art which glorified the party and its base straddles both sides.