I'm not a fan of the recent fad for PowerPoint decks full of pictures, and few or no words. While the text-packed presentations were guilty of a different sin, the answer is not to remove so many words that someone looking at the slides post oratio can't figure out what the presenter was saying.
In other words, your slides are a UI. The user experience must fit the use cases, including people reading your slides, instead of listening to you talk. You could jettison that use case altogether--if someone didn't hear the presentation, too bad for them. However, I'd bet that most speakers don't want that much economy of communication.
If you're teaching a creative writing class, and you're coaching a chronic blabbermouth, you might want that person to learn how to write haikus. That approach might help them write shorter novels, but they're still going to write novels, not haikus.