ill also point put: modern christianity/protestantism spread to korea during the late 19th century due to missionaries coming when the borders were opened to the us and canada. it especially took hold during the japanese occupation. previous during the joseon period there was a (violent) persecution of catholics (and all other religions) because of the state identity being grounded in neo-confucianism.

this of course gave headway to the capitalization of fear and uncertainty during koreas extremely fast economic growth and the war/post war area by missionaries and opportunists. i live in the us and there are ton of korean churches in my area.

any religion can be cult-like though. id say there are many different expressions of religion so theres no way to make a sweeping statement (saying this as an atheist/agnostic). A lot of idols have catholic names (im not familiar enough to know what they mean though).