I would like it to update the chart as the script runs. I found out that updating the chart data table WITHOUT activating it first seems to work, although for some reason it's slower.

Yeah that makes sense. If you are in editing mode in PowerPoint the refresh objects works differently then when you are in presentation mode. If you are in editing mode it should work no problem. Presentation mode though, you may need to call GoToSlide in your VBA right after updating the chart to get it to "refresh"