In terms of whether or not DE is an RPG, there will never be an answer. Regardless, the devs marketed it as such, so that's probably how people are going to look at it in the broader gaming spectrum. Genre categories like 'RPG' are too broad to have a clear meaning. Or at least that's how I see it.
In terms of political opinion, one thing I will say is that the authors seem to suggest that every ideology is inherently flawed because they are made up from humans. And of course, as is well established, humans are incredibly flawed animals. The game seems to take the piss out of everything Harry can believe in. Every person who has radical beliefs in ANYTHING (such as the racist lorry driver, or the fascist guy, or the communist deserter, or the race-supremacist, or the ultra-centrist moralist) are played out to be fools, more dedicated to the idea of having their ideology rather than their ideology itself.
The centrists are really just husks that don't take a stand on anything and hence have no values. The fascists are basically blaming their problems on whoever for essentially no good reason. The communists are generally shown to be somewhat naive, and bitter (all of these are vast oversimplifications, of course). Harry can adopt some of these opinions (centrist, communist, fascist, or some type of libertarian). Every time you do, you essentially become a caricature of those beliefs. The joke is the lack of nuance. The butt of the joke are the extremists - at least, that's my interpretation.
So, all this to say, the game has a lot of nuance to it. The developers are most certainly left - no question about it. So yes, leftist literature definitely informed a lot of the game. But remember, it criticizes itself as well.
Another interesting theme of this game seems to be 'balance'. Not pure centrism, as moralists are clearly just corporate husks masquerading as humanists, but the idea of defining yourself beyond your ideology. The human experience is so much more than politics, after all. I love how Disco Elysium seems to celebrate this, by cheekily poking fun at HBD's (and by extension, the player's) desire for a quick and easy ideology to subscribe to, as if there isn't any nuance to life. It's such a breath of fresh air in landscapes dominated by ideologues.
I found that one of the best things about Disco Elysium is how you can gain a lot from it even without necessarily agreeing with the specific political opinions of the creators. In some ways, it goes beyond that. Through their in-depth understanding of Marxism and Communism, they can criticize it through a lense that only someone who truly understands the principles can. I'm not a communist by any means, but I still deeply appreciated its message. Even if you heavily disagree with it, exposing yourself to other opinions is a healthy way to gain perspective on your own views.
This thread has been an interesting read, so thanks for starting it Jenkem!
I love you all.
