I don't have a public feature matrix available right now but can look into it.
WAB not being updated to the 4.x JSAPI.
The latest web apps coming from esri are built off of the latest JS API which is version 4.x. WAB and Map Viewer Classic are using 3.x. New features like group layers, effects and vector symbols are only supported in the 4.x version of the API and will not being coming to the 3.x version. This means these new map features will not be supported in these apps.
Experience Builder and WAB questions
- Experience Builder is a web app to build configurable apps with widgets similarly to WAB
- WAB Dev updates - I would refer to that team and forum for their scheduling on updates but this will also be limited to 3.x builds and not the latest API.
- I dont know of the parity matrix between the two apps.
- Web Maps will work in both older and newer apps but some features will be dropped bc they are unsupported like the ones I mentioned about. The features that I did mention above will work/show up in Experience builder bc it is using the same version of the JS API.