Regardless of how lyrical or rhetorically gifted they are in conveying big ideas, any candidate can do a good job of giving a speech if the goal of a speech is more than just delivering it well but achieving some end, whether it's convincing people of some issue or persuading them about you as a person.
When a joke works, it works. It can make a point in a really simple way; it can be a great little sound bite to put on television or share on social media. Humor has this incredible power in how we communicate about politics now, in part because there's something natural in the way it's communicated.