No. Not every app needs to become an operating system for life. We can have multiple apps on a device with little to no inconvenience. Carrying multiple devices is much more cumbersome.

Ideally they don’t, but they have - go live in Asia or South America for a bit and you’ll find spots where this is the model, and Signal can’t easily (or at all) reach those users without competing.

Are you saying people in those regions only able to use one app on their device / phone?

You'd be suprised, WeChat for example is almost a platform of its own.

You know I'm not saying that. ;P

That's just how it winds up working there.

It's not. First of all, a phone is physical hardware, Signal is an application.

Does Signal also need a music streaming integration? Restaurant listings? A torrent client?