distancing themselves from the USSR and PRC while fetishizing Cuba and Vietnam
Not so sure about that second part. I've heard plenty of Trotskyists call Vietnam "Stalinist". Sometimes they even call Cuba that. And Maoists tend to have the same problem with Vietnam as they do with China: they call it capitalist roader and revisionist for its market reforms. I've even seen that accusation leveled at Cuba for its own reforms.
Trots and Maoists are two sides of the same ultra coin. They criticize socialist states from seemingly different ideological directions, but they share a functional commonality: ultra-leftists advocate for socialism/communism in theory while always opposing it in practice. Ultra-leftism thrives on dogmatic and puritanical thinking.
The result of this kind of detachment from material conditions is to sabotage the success chances of socialist movements in the real world.