If it's better to use "simple, straightforward words" then why do we spend so much time learning vocabulary?
It should be obvious to you that your list of A/B words have similar definitions, but not exactly the same definitions. Knowing a word and using it in a way that means exactly what you want to say leads to better communication. Using it improperly (just to be intelligent-sounding, for instance) can lead to comic misunderstanding. In daily communication, simpler is better. For advanced communication, a better vocabulary would be more efficient.
The better your vocabulary, the more likely you are to choose the right "simple, straightforward words" to get your point across to the greatest number of readers.
There are countless times when you'll need to find a synonym and then one of those multi-syllabic words will come in very handy.
All words have their place or they wouldn't have been created. It is much more efficient using simple words, especially for the majority of your readers, some of whom may not know the definition of a more abstract word. I believe Einstein said, "Keep things simple, but not simpler."
deaf can't appreciate any music other than percussion instruments
Vocabulary teaches us meaning, context and also how to spell. Try using words of any complexity or candor without these skills.
You learn the vocabulary to understand what other people have written- especially in academic subjects. When you are doing creative writing, you're writing something people will read for pleasure, and it shouldn't take as much work as reading academic material.