Blastoidea There are layers to that. In some respects, I agree, especially if the solution to what someone wants to do affects the security model etc.
That said, again, the launcher is just another app. The same could be said about replacing the keyboard, the gallery app, or installing any other apps.
All of those things "could be a problem" and turn GrapheneOS into something it isn't by default, but they are all valid use cases, otherwise we'd all be using GrapheneOS with the default apps and nothing else.
I think that again, launchers get a bad rep cause it feels like you're changing something that's integrated into the system, but the reality is that launchers are apps specifically so you can change them. Not all launchers are going to be equal, and I wouldn't really recommend changing it unless you have a very specific use case like OP here. but launchers are fundamentally meant to be something you can change.