It sounds like you’ll be able to manage the first few integrations (i.e. TransferWise’s) through the app. But once the open API is ready & any developer can build an integration, I expect their data will feed into Monzo but in some cases, you’ll still use an app that they’ve built to manage some of their functionality.
Otherwise it would take too long for Monzo to adapt the app to enable you to do everything you need to, for each provider.
Ultimately, Monzo wants to be the hub for all of your financial services though, to save you having to use multiple apps (most of the time) to manage your money. I hope that makes sense! 