I think that vocabulary matters much more than grammar to use a language. In many cases a learner's message with some grammatical mistakes could be understood. But without vocabulary knowledge it's impossible to express one's thoughts and to understand a message. Often it is not possible to guess vocabulary meanings in context correctly and precisely. The more vocabulary a learner knows how to use correctly the easier it is to convey a thought in a language in speaking, in writing and to understand the reading and listening content. Please read my posts here on English vocabulary issues.
I used to agree.
Learning loads of vocabulary is just as useless as trying to master perfect English grammar. The best way to get functional in a language is to learn phrases in context. And that is only possible through first-hand exposure to the language. The more of those template phrases you learn, the easier it will be to put them together in grammatical sentences.
I've always supported learning and practicing set phrases in context. In my opinion vocabulary should be learned and practiced first through input (listening and reading), and then used through output (speaking and writing) on each real life topic. But vocabulary is a broad concept; it includes not only phrases, but also separate words, idioms, proverbs, sayings, etc. Please read my post here titled "Difficulties in vocabulary learning".
I highly value comprehensive monolingual and bilingual thematic English learning dictionaries that arrange vocabulary by subject matter and topics, and provide word meaning explanations with usage examples in several sentences for each word or phrase meaning.
I also know website links to thematically arranged vocabulary, including phrases and idioms.
You can combine reading texts (from newspapers, magazines, books, online, etc) with reading thematic dictionaries to accelerate learning of vocabulary in addition to listening and speaking practice.
In my opinion a learner should be selective in choosing first the most frequently used vocabulary to learn from thematic dictionaries for his/her language needs and use. This also applies to content of materials for listening, reading and speaking practice. Have you selected materials with appropriate helpful thematic content for your needs for listening, speaking, reading and vocabulary practice? Some planning for short (if you are busy) daily classes on your own won't hurt.
It's (as already stated) about learning/absorbing collocations.
From Wikipedia: a collocation is a sequence of words or terms that co-occur more often than would be expected by chance
Word combination strong tea sounds correct while powerful tea would sound strange.