That's fine. You can choose to use a Markdown-only editor if you prefer, even if WYSIWYG is provided with Flarum by default. However, the majority will stick with WYSIWYG, and that's exactly why it's good practice to tailor defaults for majorities, while less common preferences (such as Markdown preference) can be offered as options or plugins.
RelicSystem It’s puzzling why someone would create an account on the project’s forum just to criticize a missing feature they personally need. As mentioned earlier by others, the best approach is to propose the feature. If the community supports it (financially or vocally), the core team would likely consider it.
There's nothing puzzling about that; people explain why they can't use Flarum—it lacks critical features for them—and that they will switch to Flarum when it's addressed. This is quite useful information for Flarum developers. So it's exactly what you said: they are proposing features vocally. Thus, your paragraph is really weird and contradicts itself.
RelicSystem In the meantime, nothing prevents another developer from forking the existing WYSIWYG editor, providing patches, or even creating an alternative based on the same editor (ProseMirror). If, like me, you lack the coding skills, consider reaching out to those who do and collaborating with them.
You're missing the main point: it's too risky to rely on third-party plugins for critical features like WYSIWYG or file uploading. It's completely normal to expect these to be available out-of-the-box, especially since every competitive software provides these features in their base distributions.
It has already been stated that if WYSIWYG were built into Flarum, it would receive much more attention from the community—more pull requests, bug reports, and other forms of help and feedback—compared to being just a plugin supported by a single person, with uncertainty about its future.
I love Flarum, but I definitely won't migrate my most important communities to Flarum from other forum software until WYSIWYG and file uploading are available out-of-the-box.