In reply to Nick Halsey.

Bloat IMO isn't limited to features but also reduced performance and cluttering the UI / UX.

"Themes and the ability to change them are one of the most fundamental features of WordPress." - Agreed.

However, this happens whether the customizer gets used or not. The Appearance menu / Settings API is plenty enough. If the "Customize" option ceased to be it would make no difference to me.

The customizer and settings API are not the same to me. I use one but the other. The Customizer could live happily as a plugin even while the Settings API lived on in core. Right now it's just a growing source of irritation that I put up with because I really like WP and it's free.

I really love WP's Flexibility and Modularity but as far as the Customizer is concerned, WP is pretty rigid to me.