When Writer starts up under the default template (which is in fact empty!), it has absolutely no idea about what you want to do. Consequently, it enables the only paragraph style guaranteed to exist at this moment: Default Paragraph Style which inherits various attributes from Tools>Options, LibreOffice Writer>…
I admit this is not smart at all because Writer is already loaded from factory with numerous styles that developers thought were “universal”. However, they have nothing sacred and can be replaced with whatever configuration you want (apart from the fact that they have been flagged as not deletable).
As you point out, starting with Text Body would have been better from a user point of view. But Text Body is not hard-wired anywhere in the code.
Paragraph styles can be linked to each other through an attribute named Next Style. This is what happens when you use one of Heading n. Since their intended usage is heading and heading are usually a single paragraph, their Next Style property is set to Text Body for user convenience.
You have nevertheless a handy shortcut to force Text Body when you start typing in a blank document: Ctrl+0 (zero). And Heading 1 to 4 are hooked to Ctrl+1 to 4.
Paragraph styles can be derived from each other. A derived style inherits the attributes of its immediate ancestor and overrides only a few of them, so that when non-overridden attributes are changed higher in the inheritance line, this change is also propagated to the derived style(s).
Default Paragraph Style is the basic paragraph style, the ultimate ancestor of all other styles. It is used to set shared attributes. Modify it to set your own defaults, but never use it for typing any text.
Text Body is a direct descendant of Default Paragraph Style. Usually it differs from it by the spacing above and below distances, sometimes by the indents. Text Body has itself descendants, like Hanging Indent with a left indent and negative first line indent so that the first line extends left of paragraph body.
Yes and no. As already mentioned, Default Paragraph Style has a “technical” role of setting defaults for your documents. These defaults apply to all other styles (unless overridden specifically). So, it is not desirable to make Text Body an alias for Default Paragraph Style. This would break many internal mechanisms.
But, you can make them functionally equivalent by modifying Text Body. Open Text Body paragraph style configuration dialog and press Reset to Parent button in every tab. This will erase any override made in the style. But it will also impact all styles which are descendants of Text Body, notably the List family (List n and Numbering n).
To have an idea of the hierarchy between styles, select Hierarchical from the bottom drop-down menu in the side stylepane.
