Personally, I don't think the acting is inconsistent per se, rather that most Koreans overact a lot and characters tend to be caricatures because of that. The best example of that is Kim Joo-Ryung who plays the cray-cray lady in Squid Game. She's the queen of Korean overacting. Every movie or series I've seen her in, she's overacting.
The worst of their overacting is in their zombie movies. Koreans make the worst zombies ever. Train to Busan was great, still, a lot of the zombies felt more like escaped violent scitzos than mindless flesh eaters.
Related bit... I introduced my wife to Breaking Bad and Ozark (and BCS) and she couldn't get into them, telling me cartel and mafia stories aren't her thing (unless there's Pedro Pascal somewhere in there, she did watch and enjoy the original Narcos). So yesterday, she's browsing Netflix and we both read the description for A Model Family. My first reaction is thinking "wow that sounds like the Korean knockoff of Breaking Bad or Ozark" and my wife, she tells me "oh, it's Korean, so it should be good". I'm like "Are you f***ing shitting me?" She:"What's the problem?" "Well, for one, you skipped on three of the best drama shows I've ever seen because, apparently, you don't like cartel and mafia shows unless there's lovely Pedro in it, but hey, it's a f***ing knockoff of Breaking Bad and Ozark, but since it's friggin Korean, it haaas to be good, right?"
She was a bit embarassed when she realized her bias. So from now on, whenever she'll tell me something looks good, I'll tell her "it has to be Korean, right?"
First salvo today. My wife is petting our dog, she tells it "you're such a good dog". As i'm passing by "she must be a Korean dog"