When the creation of a presentation involves designing slides, you often have a graphic designer who takes care of the visuals and somebody else who is instead responsible for the content (the message to be communicated). In these cases, who is in charge? Who should have the last word on how to create the presentation, especially when the two roles have different views?
In an ideal world, neither of them is in charge because they both have a lot to learn from each other. There should be a healthy cooperation between the two roles based on mutual respect. Remember, if it’s appropriate to illustrate your talk using visual aids, then your presentation needs both engaging content and also a captivating design that supports and amplifies your content.
However, the reality is that we don't live in an ideal world. Sometimes there is tension between different roles. For example, the designer may want to go for a certain design choice which is not what the person responsible for the content was looking for. What do we do then?
In those cases I would give the last word to the person who is in charge of the content, which could be the speaker herself or somebody else supporting the speaker. I’m not saying that she should also decide how to design the slides (that’s why you have a designer in the first place) but the story always comes first.
The designer's job is to support and amplify the story (which can be super powerful) but not to create it.
Story first and foremost, but with a huge respect for design.