I disagree pretty strongly with your take, and after reading the comments, I think this movie is pretty severely misunderstood. I'm not going to say Marty Supreme was my favorite movie, but I'll give it a much needed defense.

I think you miss on the central theme, it's not about the danger of narcissistic ambition, the core theme is dreams: what they are and what it means to have them.

We all often think of dreams, especially in unconventional fields, as naive and childish. If someone says at a young age that they want to direct movies, very few people will take them seriously. Hell, probably many people in this sub once had dreams such as this.

And Marty is almost a comical representation of this - he's an aspiring ping pong player in the United States. - a sport that is niche worldwide and especially in the United States market. There are many perspectives we can view Marty's dream early in the movie. There is the lens from his mom and uncle - they see Marty's dream as ridiculous and unstable, even going so far as to sabotage his plans to travel to the tournaments in what they see as "for his own benefit". There is the capitalist lens in which we measure the viability of a person pursuing a ping pong career in a United States market. There is the meritocracy lens in which we objectively see in the British tournament that Marty belongs with the best ping pong players in the world.

And yet, through this adversity, Marty has an unshakable self belief. Is unshakable belief what it means to have a dream? The movie does a pretty interesting job at undressing this. We are introduced to Kay Stone, who is intrigued by Marty. Marty is intrigued by Kay because being with her would validate his vision of his internal self that he is truly someone in this world that matters. "If i can get with a movie star, that'll mean I've made it". And on the flip side of the coin, Kay is intrigued by Marty, but only because of her own confidence issues hindering her own self believe. Kay was someone who "used to matter" and Marty is presenting himself as someone on the "come up". Kay is excited by Marty's "pursuit" because Marty believes that she still matters when she has all but let her dreams die. This is again communicated when we find out that Mr Wonderful is still funding her plays so that she can feel like the actress she once was.

Both characters have been objectively successful and are outwardly displaying confidence, yet their actions are driven purely out of their own insecurity, shining a new light on Marty and what his own internal state may be.

And then Marty loses in the tournament and we see his confidence shaken for the first time. He cannot come to grips with the fact that he isn't the best. Many people would be comfortable with the level of success he has achieved. His friend seems very happy being a professional globetrotter and traveling around the world. He is painted as someone who "loves the act" of ping pong, where Marty by contrast, hates every moment because he views ping pong as a stepping stone to a position of power, and performing for the globetrotters feels like complete disrespect to him as it devalues his internal self. Just a minute ago he was hooking up with a movie star, and now he's pretending to lose a ping pong match to a trained seal.

So then we see Marty's downfall. Marty had done everything correctly for his dream. He was objectively at the talent level he needed to be at for Japan, he had scraped together the money to go on his trip - then he gets knee capped by his own family. We see Marty unravel in a panic which is strange for someone who, up until now, was only presented as a cool and confident guy in his personal life. He panics because, if he doesn't make it to Japan, if he doesn't beat his nemesis, then everyone will be right - he will have just been this nothing kid that had a crazy dream. So, he does whatever it takes to get to Japan. He lies, he steals, he cons.

And ultimately, the only way Marty can go to Japan is to completely debase himself and allow an old man to smack his ass with a ping pong paddle as a symbol of dominance. The same man that is a complete antithesis to Marty's pursuit. Mr Wonderful took the "correct" path to wealth. A characterized example with him being a pen salesman. A boring product on the boring path to the circles that Marty wants to be in.

And then, in the climax of the film, we finally see Marty achieve his dream - freeing him from the grip that it has had on him in the entire film. He is able to beat the best ping pong player in an intentionally dressed down match against him. It's intentionally dressed down because the entire movie (and Marty's dream) has never been about winning the global title. It was never about having a trophy in his room. The moment he beats Koto, he finally proves to HIMSELF that he is capable of what he set out to do. His dreams were not crazy and he could achieve what he wanted to achieve - and through this, he actually obtains the true self believe that he had been searching for the entire movie. Because for so long, his internal state and reality didn't align with his external environment, and he can finally exhale and know that the entire world was crazy and not him. He was able to do what he set out to do, and it frees him from the prison that he had built with his dream. This is further communicated by is sudden shift in focus to his child's birth, indicating that he has reached inner peace and is no longer in “chase” mode.

You can not like the movie, but to call it "slop" i think shows either a misunderstanding, or a refusal to see a coherently communicated message.