I developer of the HA Community app. I can give you some insights.
But the Athom app you are using is not open source. I know some technical basics about the HA connection but can’t check the app code.
Difference:
Athom app (official):
- useable for HomeyPro anc Cloud
- imports HA devices with their entities
- simplified, only common entities are supported
- no possibilities to adjust devices or entities
- connect only via port forwarding (running in the Athom cloud)
Community app:
- only for HomeyPro
- running on Homey, so local connection
- imports HA entities based on domain
- support most (nearly all) standard HA domains
- customizeabl devices
Both are connecting to HA via Websocket.
Athom app uses oAuth, Community app the HA longlived tokens.
Connection is bidirectional via Websocket (instant updates from HA).
As far as I know, the Athom app also uses Websocket to read the device list. So I wonder why you get a device list, but no device content. But without code we can’t find the reason 
But… When you are testing the Athom app on HomeyCloud you will never see all possibilities you will get with a HomeyPro.
We can only help you out with additional information. If you want to see details about the Community app, yo can taka a look at these pages. You can also ask other users in the HA community thread.
I hope that helps a bit providing you with some additional information for yoru decision 
