Yep, I have to agree with most of the comments regarding the survey being comprised of mostly Developer feedback. I believe most Devs would probably prefer to work directly with files/code instead of using the Customizer >>> https://codex.wordpress.org/Theme_Customization_API#Developing_for_the_Customizer. Seems to me that logically folks who build, modify, customize and create new websites for customers would most likely be the highest percentage of Customizer users.