I find customizer a pain in my ass. I create site for business owners, for creatives who want a showcase, for small ecommerce experiments. They want one theme, and they want it finished. They don't want to upload a logo or decide on a different color for their links. I used to rely on Suffusion for an incredibly flexible framework. The opinions section was laid out logically, and I could finish my tweaks with custom css inserts. Now I'm using WP-Forge and child themes. I can skin a site pretty quickly editing a css file. But I am constantly being tripped up by the customizer, and its overrides. It would be WONDERFUL if there were a way to turn it off in cases like these.