Android widgets like Vista widgets, OSX widgets, or KDE widgets failed at their vision because it's usually easier to open an application when you want one.
The webOS card interface scales to tablet beautifully (I think it was actually better on tablet) and with some additions would scale to desktop as well.
The UI was successful (IMO) because it wasn't actually different. Someone (at Nokia IIRC) once compared iOS navigation to having a house where every door faced outside and you have to go outside to go around to the room you want. Android made the same mistake. Both have taken step after step to deal with the effects without really addressing the cause.
On a desktop, opening apps is secondary. You have a few favorites in your dock for quick access. After that, you either open your start menu or launchpad and go hunting else you Cmd-SPC and type the name. Once you have everything open, switching and managing applications is the name of the game with lots of tools to make this happen.
The default paradigm in webOS is the same. A dock of favorites with an app drawer plus JustType to find less-used apps. Aside from that, managing apps is front-and-center. Compare groups of cards to OSX horizontal spaces. You go from group to group and managing apps is the default. Once again comparing to OSX, webOS has a consistent menu in the upper-left and a settings menu in the upper-right.
Android and iOS now try to mimic this, but it's always a secondary feature. Home is default with app switching being someplace you go to to see your list of 100 "open" apps. Both have decided that users who are perfectly capable of using a menu on their desktop are incapable of doing so on a phone.
Another not really mimicked feature of webOS was its service integration. Having all your different accounts working together in one central place seamlessly is an experience nothing comes close to.
Even comparing to the web they were ahead. EnyoJS was/is a component-based framework. You could compare it to React with manual view updating (which is actually more powerful if less easy on the developer). This was in the backbone, knockout, early angular days.
The flaws of webOS were blatant and fairly fixable. They used Qt for the GUI, but didn't allow native apps to be built using it (and didn't have a native SDK until way after they should have). They use Qt's version of v8 and webkit which were terribly out of date and (as a result) much slower than they should have been. The underlying Linux OS never had even basic optimizations put in place. The hardware was sub-par and memory was too restricted at the time. There were also rough edges in the UI, but nothing worse than iOS or Android at the time.
Today, loads of phones have more than enough memory. The processors are fast. Web standards now have things like wasm or webworkers that make apps much more powerful. This is the time when webOS really could shine.
In a day of 4+GB phones running the fast processors of today, much better web standards w a web phone really is more relevant than ever.