I'm not convinced. Show me the results of A/B study along any set of UX metrics you'd like to measure. The author uses the term "performative" without any performance metrics.
Going all the way back to Parc, pre-OSX Mac OS, VRML, OpenStep, and countless widget and windows managers for Linux (anyone remember Enlightenment (https://www.enlightenment.org/about.md ?) we've had deep dimensional design, animations, and heavy-weight skeuomorphics multiple times and have always returned to shallow static dimensional design for mass/generic applications.
I suspect it amounts to less overall mental effort which improves workflow speed and, thus, a greater perception of interactivity.
Maybe deep dimensional design will return when cheap and ubiquitous AR (augmented reality) or VR becomes a...reality, but I don't see it happening with 2D displays.
As someone who worked in IT support icons can be award winning and you'd still find people who will have a hard time understanding their meaning when there is a label written underneath them. People are lazy and don't read text in computer programs. Sit next to a user who clicked away a warning and ask them what it said.
As a former freelance graphic/web designer I'd argue that the style of icon is much less important than the organization of those icons. E.g. some software will put 50 icons seemingly randomly into a toolbar and let you play a game of "find the right one". The quality of every single icon becomes utterly meaningless then as the organizing principle is wrong.
That means first an icon bas to be the right choice and be used in the right context, then we can talk about readability and how well it clicks and stylistic questions come dead last. Some people think graphic design is about coming up with cool looking styles. That is literally the opposite of what good graphic design is.
Any A/B study would look at conversion metrics ("did people spend more money?") rather than user enjoyment. People don't go on Airbnb to browse or hang out, they book a room, pay and that's it.
Between current flat turds and Keramik/e16 there are sensitive settings:
-Motif UI
-Plastik
-Platinum
-GNUStep/NextStep
-BlueCurve
All of them have clear outlines and contrast.
On Icons, Tango and Tango2 from Gnome are unbeatable. Maybe just Haiku/Be icons can truly be over Tango.