Those are all orthogonal concerns to the way the text editor behaves. You could have a structural text editor operate on plain text files and a dumb text editor operate on AST, you can do plain text diffs of ASTs or diff AST parsed from plain text files, etc etc...

Some of these have existed historically (or even still exist).

Paredit-mode is a structural text editor that saves and loads plain text files, Smalltalk was typically implemented as a dumb text editor but then code was saved as compiled binaries (which meant you couldn't save your functions if they weren't syntactically correct but you could have unsaved syntactically broken functions), Mathematica represents its code in a weird format that might as well be binary but copy/paste converts to plain text, there's one git plugin (don't remember the name right now) that does syntax aware diffs even though git deals with plain text...