If it's different parts of the same system I really don't like if it gets split up to multiple apps. Take steam, there I need two apps, one for the general store and it's functions and one for communicating with my friends. In that case I'd rather would have one app that fits all.
But if I don't need several functions of an app and they are also hurting the experience with it, I'd rather would have the sourced out to other apps.
The thing is, in systems like WhatsApp we don't decide what is the best for us, but WhatsApp.
Maybe integrating some features is better, maybe separation.
Or maybe third way, separated things under one package (for example all-in-one packages like Nextcloud or Thunderbird).