I was thinking something similar while reading the article. Studying Japanese it's easy at first, and even kanji is easier than it appears, but eventually there is a huge increase in difficulty when you get to advanced grammar and conjugation, which changes based on tense, voice, imperative/not, gender, ranking, politeness level, etc. Every language is like this, although every language has its own unique quirks and difficult points.

Learning it is also kind of like learning physics in high school. After a few years you realise the first things you learn are a bootstrap to get started and not actually used in daily speech. Simple example: You hear the words "anata" ("you") and "sayonara" ("goodbye") one time in a month, but you will use them all the time in beginner Japanese class.