I would say that highly intelligent people are typically gifted communicators, yes. And it is quite fashionable, I think, to assume that anything that seems complex or any idea that you don't immediately understand is just nonsense from someone who is trying to look important. If somebody uses a long word, for example, it's not because they wanted to use the right word to express their thoughts clearly. It is because they're trying to look smart. Philosophy, in particular, suffers from this, because a lot of philosophy is hard to understand. I think that this situation came about because of egalitarianism and democracy; if we're all equal, and somebody else says something you don't understand, then clearly that person is just being pretentious. It couldn't possibly be the case that they just happen to understand a difficult idea because they've put in the time. No, they're just pretending in order to look smart.

In reality, however - brace yourself - there is a shocking truth here that belies the common wisdom: sometimes there's stuff that is hard to understand. As in, sometimes there are ideas that are really hard, so you have to think about them a lot to figure them out. It's kind of similar to how there are foreign languages, and those languages look like nonsense until you figure out how to speak them. Some ideas sound like nonsense until you think about them really hard.

This is where Kant comes in. Kant wrote books that are hard to understand. This is not because Kant is a horrible writer. It's because his ideas are really hard. And when people assume that his books are hard because he's a bad writer (or worse, “pretentious”) that makes me feel very annoyed, which is the reason for all the snide condescension in this answer. It's not aimed at anyone in particular, though.