You nailed it! I was a middle school teacher for about 6 years, and I would have been fired the first year if I lectured to the kids during our class time. I’ve been in church all my life and can vividly remember only two sermons.
I once helped plan a men’s retreat and we ditched the lectures and did small group discussions. We received high approval marks on a post-retreat survey.
When I was a child, my dad helped plant a church in which we often split into groups during the service to discuss the Bible. Great! And I recently heard a missionary to Alaska explain how he ditched longer sermons, put his pews in a circle, and held discussions and conversations with the congregation after a short lecture.
I don’t know the history of the sermon, but I’m going to assume at one time it was extremely useful for an educated religious teacher to teach less-educated congregants. I think that dynamic is somewhat useful today. But I think it less useful than we like to think.