I will echo what Christian Nelson, Andrea Whitmer, and G said above. You asked the wrong people. Of course lots of Devs don't like it. Many of them complain about anything WYSIWYG in general.

As a designer with a fair amount of front-end skill I prefer writing my own files when doing my own building and customization. However, for out-of-the-box theme use, even I'm starting to appreciate the customizer and those theme companies that use it well.

I'm not sure about plugin/core and I'm also not sure about how it also includes menus and widgets. However, I could envision it being a place where we could actually use it to more easily restrict what an end-user is allowed to do when you don't want to give them access to everything.