I am pretty sure that with proper tools you can achieve more or less acceptable quality. But the goal of all this tools is to provide you WYSIWYG experience. The built-in table editor in Emacs is clearly a WYSIWYG or at least close approximation of it.

But again all this is about additional tools. Main goal of Markdown & friends is to achieve at least some WYSIWYG when the only editor that you have is <textarea>.