Many apps do have diseconomies of scope — they have too many features, and are therefore hard to use. And the company spent more resources to build a more featureful app, like hiring more people, but this extra investment has had a negative return.
Overspecialisation also causes problems, like engineers who don't understand user experience or empathise with the user or even stop to ask whether the flow they're building is needlessly complex. Or designers who propose ideas that are not technically feasible given the platform.
If you can increase scale without increasing scope, like WhatsApp supporting 900 million users with 50 or so engineers, great. If you're increasing scope in order to increase scale, you can't assume that the former leads the latter.
Overspecialisation also causes problems, like engineers who don't understand user experience or empathise with the user or even stop to ask whether the flow they're building is needlessly complex. Or designers who propose ideas that are not technically feasible given the platform.
If you can increase scale without increasing scope, like WhatsApp supporting 900 million users with 50 or so engineers, great. If you're increasing scope in order to increase scale, you can't assume that the former leads the latter.