As far as I understand your main assumption is that vocabulary acquisition is a smaller problem than grammar (i.e., how to express your idea). I have to disagre

As far as I understand your main assumption is that vocabulary acquisition is a smaller problem than grammar (i.e., how to express your idea). I have to disagree. While this might be a problem for some people, for others acquiring thousands of vocabs is a huge problem in itself. Beside personal problems and preferences there are also big differences depending on the language you are learning and the languages you already know. An English native speaker learning French has much less vocabs to learn than an English native learning Chinese. Additionally to memorizing huge amounts of vocabs I also find that learning phrases is very helpful, but more as a second step. At least for me it works like this. "Memorizing a bunch of vocabulary" is exactly what got me started to finally improve my Chinese.