I share your view of the [Quick] Styles Gallery. It, too, has been degraded by the "New Experience" view.
New Experience/Visual Refresh Preview - Microsoft Office - Offic e 365 - Turning it On and Off I suspect that some of the developers at Microsoft do not understand the utility of styles.
The Quick Styles and Quick Style Sets can be very useful.
[Quick] Style Sets and Word Themes in Microsoft Word.