Addon manager should have button to update from Asset Store / Addons page
First of all every addon available in
asset store should be available in addons page but not downloadable if the user didn't buy it yet.
Then Construct3 should be able to detect those addons from their own addons page and show option to download them all when a project needs them instead of just alerting "Missing addon".
Then Construct3 Addon manager should have buttons to update to latest version of the addon like the example picture.
The addon infrastructure is very beta right now in my opinion. The end user needs to manage a lot outside of the Construct3 editor.
https://www.nuget.org/ could be taken as example how it should work.