This is – for better or worse – how Tiptap works. It is a structured editor based on a schema, which is ideal to use for JSON output, which is its default mode.
It will not allow even a single element out of place that is not defined in its schema, which is where “capabilities” come in. They add the appropriate extensions to the editor, extending its schema.
For the most part, this means you will get clean, maintainable HTML.
But for those who’d like to have unrestricted HTML editing, TinyMCE is likely the only viable option on the market. It is well-supported in Umbraco 16 and presumably Umbraco 17 as well: