From a Pluralsight author, there’s a difference between talking and teaching.
Overall I think it’s good. I try to keep some of these points in mind when I talk, though I haven’t always kept the agenda slides in. I’ve tried them in a few places, and I like them for pacing myself and transitioning things. It also reminds me to ask for questions.
I completely agree that “You probably already know this” is poor technique, whether writing or speaking. Don’t assume people know something, and if you have doubts, ask.
Speaking well takes practice, as much for your delivery, as for the comfort you get after lots of talks. The better you feel, the better your talk will be for the audience.