I believe your issue is similar to the one I posted here (45087).
I believe ngOnChanges() is the “scalable” way to do change detection and that it is similar to $scope.$watch and that there is no “more scalable” way (please tell me if I’m wrong). I also believe you don’t need an @output EventEmitter/subscriber at all (see how I do it in my post). However, what I’m doing currently does not fire ngOnChanges() as it should, it seems. Let’s wait and see if there’s a response to the issue I just posted, it may answer your question.
There’s a lot of relevant info here on change detection - still sifting through it…