The publish editor for articles & files in Horizon is (in my view) an inconvenient mixture between WYSIWYG and html access that overcomplicates many simple tasks.
The old editor in v5 was far from perfect, but it allowed creating an article in the WYSIWYG editor and then editing the html of the entire article to add more complicated styling (e.g. a class name to a table to get a different format). I also used the ability to access the full html code for things like advanced search & replaces using regular expressions in an external text editor, and for things like transferring a prepared update of an article from a test environment to our live environment in a few seconds.
The new editor no longer allows any of these things, as it forces a single html element per "block", does not allow viewing the html of the entire article, and does not allow content created in the editor to be converted to html. This is extra inconvenient because it seems to be missing some basic functionality (such as adding a link to a relative url, formatting images outside of the editor, adding a class name to a table, etc.).
To work around these limitations I will most likely write all articles that require even then slightest bit of html adjustments fully in html and put all of this in an unnecessary container div in a single block, bypassing the functionality of the editor completely. This can't be the intention.
The ability to edit the html of the article in its entirety, regardless of whether elements have been added by the editor or as direct html, would go a long way to wards solving this problem.
Incidentally, I find the markdown-editor in the guides section more convenient. The WYSIWYG editor is a bit more limited and writing markdown is not as intuitive to some people as a real WYSIWYG editor, but at least this allows the addition of html code at any arbitrary point in between the markdown.