It really depends on what your userbase is like. I can give you my perspective if I was your target user.
As somebody who often visualizes survey data often in Mekko Graphics and Excel/Powerpoint charts, I would say customizability is key for advanced users. My most frustrating time using these programs is when I am trying to change something that the program tries to automate. Excel/Powerpoint charts default to the color schemes of the document theme, for example, and Mekko automatically sizes and positions all labels, but often doesn't do a good job. Don't even get me started about Mekko's default number formats. The reason I need customizability is that I spend a lot of time looking at the data and thinking about it, and I decide what the story is that I want to tell with the data. The visualizations are citations in a story, and I want to present a simple view that tells exactly what I want it to tell.
While there are an array of guidelines that people should follow to represent data with the least bias (for example, presenting percentages should always be done on a scale of 100%) and giving ultimate flexibility can allow a researcher to violate those guidelines, ultimately best practices can't be controlled by the software, they can only be instilled through a community.
Having seen many non-experts also make and present Excel charts, I think they crave customization as well, but there needs to be a good starting point that they customize from. I usually know exactly what type of chart I want to share before I start building it in Mekko, but a novice user probably needs that automatic guidance like defaulting to a line chart with time series data.