Oh man, despite its technical flaws (crashes and bad performance), I still really miss the Dashboard feature from those old Mac OS versions!
Just recently, Apple have started reintroducing desktop Widgets to macOS. But I wish you could make them work like the old Dashboard, ie instantly go to them with a swipe gesture or a Fn-key press.
The old Dashboard was feature just so fast and easy!
I understand why they dropped the original Dashboard, its widget platform was a technological dead-end. But now that widgets are back it would be awesome if they made the new widgets work like the old Dashboard again.
If you have any part of the desktop visible (e.g. to the left or right of the dock) you can click there so it hides all windows. I'm not sure if you need to enable this somewhere.
Also, there is a trackpad gesture to show the desktop: Keep your thumb stationary and use three fingers to swipe away, as if zooming out.
The use case for me for widgets is to display information I want to look at very briefly and then have go away again.
It ought to be pretty simple for Apple to add a "special" desktop for widgets to the left of the first desktop. This would match both the old Dashboard behaviour that I miss, and the way that widgets work on iOS.
(And the gesture you describe isn't "show desktop", it's "show all windows", though I'm sure it can be configured in macOS settings!)
And, amazingly, was HTML/CSS/JS based (for widget development).
My headcanon is that this was secretly a test run for what an iOS IDE would have looked like under the original (pre-iPhoneOS-2.0) model where there was to be no native SDK since Dashcode 2.0 does actually include the ability to target iPhone Safari.
Even today Amazon somehow managed to make the Luna web client work on Safari, which shows that with an appropriate server back end you can stream some fairly demanding games (and by extension, almost anything) into a web app.