The drive to push everything into the customizer seems to drive people into a religious type of zeal instead of evaluating technical merits, which bring strange enhancement suggestions like putting an non dismissable warning in the widget admin screen https://core.trac.wordpress.org/ticket/40830.
So maybe a explicit explenation is required why people prefer (sometimes) the widget admin screen over working with the customizer
- Customizer is slow, widget admin is fast(er). In the widget admin there is no need to load all the JS related information that the customizer needs to be able to manage the other aspects of the page which are unrelated to widgets
- It requires less clicks to get to the widget admin. To get to the admin only two clicks are required 1. login 2. navigate the menu, while with the customizer you need 1. login 2. go to the front end, 3. click the “customize” button, 4. click the “widgets” button.
- No, the customizer short cuts to the specific widget admin are not really faster. In the admin page it requires 2 click to get to the admin page, two more to open the sidebar and the widget, total 4. On the customizer it requires 3 clicks just to get into the customizer mode, then navigate to the page which includes the widget, then locate the widget on the page (in twentyseventeen a lot of scrolling will be required) and only then you get to the promised land.
This is not to say that the customizer is a pointless thing, but it for sure do not have good answers for many valid mainstream use cases. It is better to stop the zealotry and improve the widgets admin screen (add revisions to widgets and sidebars, widget duplication and the like) instead of spreading FUD about it.