Understanding Flutter Dependency and Build.gradle relationship

I'm following this guide on adding Firebase Messaging to my simple Flutter app. Within the guide it states to add the following dependency to [app-name]/android/app/build.gradle:

implementation 'com.google.firebase:firebase-messaging:<latest_version>'

It all works fine. But i'm wondering why must one do this when the required flutter plugin "firebase_messaging: ^7.0.3", which is already added as a dependency within the flutter pubspec.yaml file, has already stated within its own build.gradle file the following:

implementation platform("com.google.firebase:firebase-bom:${getRootProjectExtOrCoreProperty("FirebaseSDKVersion", firebaseCoreProject)}")
implementation 'com.google.firebase:firebase-messaging'

I, of course removed the line within [app-name]/android/app/build.gradle to see what would happen and got the following error message:

*Application.java:14: error: cannot access FirebaseMessagingService
        FlutterFirebaseMessagingService.setPluginRegistrant(this);
                                       ^
class file for com.google.firebase.messaging.FirebaseMessagingService not found*

So is the rationale then whatever is a dependency stated within a Flutter plugin means it is only scoped within the flutter application it is attached to (everything within the LIB folder)? And if i make any changes outside this area (ie. within the root Android folder then i must deal with build.gradle and such?