A well-given talk should not require its contents to be summarized as it is being given. Pictures are worth a thousand words, so technical diagrams are an obvious exception (there are others) to that.
[1] https://skillsmatter.com/meetups/11368-an-evening-with-uncle...
Obviously a lot depends on your audience. Slides at an academic symposium can be dense enough that you can get the gist of the talk from just looking at the slide deck, slides for an introductory talk on a subject should be more like the list of contents in a book.
If you can come up with slides that make it easier for your audience to follow you, go for it.