If you've come to look at a given architectural style (or any object for that matter) in its abstracted, ahistorical form, then you may not find much value nor truth to what it actually signifies. You must instead look at the material conditions that led to its creation.

First of all rutalist architecture emerged in the USSR after the end of WW2 after the economy and the entire infrastructure of the country were entirely wiped out. Simplified construction techniques using concrete were revolutionary in the sense that they were efficient and easy to streamline on a national scale for millions of people on the one hand, while being cost effective on the other hand. Whilst the rate of homelessness was not decreasing (if not increasing) in capitalist economies, socialist countries were at the vanguard of providing free housing for everyone.

In short, brutalist architecture was shaped by the material conditions of the post-war era and developed further as the economy progressed in later decades. This is simply because policies and social and cultural phenomena are not the mere product of ideas and thoights as much as the material conditions which are the basis for every human movement.

Secondly, the term "brutalist" does not give credit to what the Soviets and other socialist countries have achieved in the architectural fields. Most pictures that are publicized on the Internet picture either abandoned and unmaintained buildings or pictured thata are taken in the gloomiest period of winter, since this id what is believed to fit the narrative or the "aesthetics" of socialist architecture.

Lastly, in reality there isn't really an artistic style that dictates what leftist architecture should look like. If you search through pictures of Soviet architecture or even DPRK or PRC architecture for something recent, you will find that they vary so much in colors and shapes, because it all depends on the architect's individual and distinct taste. Rather, what distinguishes leftist (or your so-called "authoritarian") architecture is that it serves the needs of the proletariat, contrary to capitalist societies that boast about their individualism.