Most of my clients actually know how to present visual slides. Their problem: they don't have the slides. But once I create them, they get used quickly to the new presentation format without a lot of training. This is probably because they can identify with the target audience. A CEO pitching a startup idea is the sort of person you would pitch a startup idea to.
Scientists have a double problem. Yes, their slides need work, but the bigger problem is that they often need to cross into a different audience type than they are used to presenting to. Scientist, engineers, lawyers, have their own language for talking to each other, which can actually be every effective. But if you put a scientist with newly designed visual slides in front of an investor audience things start to break down without the proper training.
When deadlines were very short, I have recommended these clients to stick to their existing slides and practice their delivery, postponing the make over of their entire slide deck for the next conference a few months down the road.
Art: Louis Pasteur by Albert Edelfelt, 1885