Short answer, yes. Specifically, it would be quite hard to use an external editor component for Confluence because of the underlying ADF format.
There have been some advancements in the 2 years since I answered. For one, there is now an Atlassian supported editor component that Forge apps can use. That component does have some parameters that allow developers to toggle various features. There is also documentation specifically titled extend the Confluence editor.
Even with all of that, none of these allow a developer to directly replace the editor (neither for Jira nor Confluence). See following:
In general, the UI/UX Design strategy for Cloud no longer allows for the replacement or removal of Atlassian provided components. You might use above tooling to provide a parallel experience but those features cannot change the core editor experience.