Yeah suppose you write a simple config language like:

  let a = 12;
  let b = a + 5;
  ...

Tree-Sitter will give you a tree like

   Node(type="file", range=..., children=[
     Node(name="let_item", range=... children=[
       Node(name="identifier", range=...)
       Node(name="expression", range=..., children=[
         Node(name="integer_literal", range=...)
   ...

Whereas Nom/Chumsky will give you:

    struct File {
      let_items: Vec<LetItem>,
      ..
    };
    struct LetItem {
      name: String,
      expression: Expression,
    };
    ...

Essentially Tree-Sitter's output is untyped, and ad-hoc, whereas Nom/Chumksy's is fully validated and statically typed.

In some cases Tree-Sitter's output is totally fine (e.g. for syntax highlighting, or rough code intelligence). But if you're going to want to do stuff with the data like actually process/compile it, or provide 100% accurate code intelligence then I think Nom/Chumksy make more sense.

The downsides of Nom/Chunksy are: pretty advanced Rust with lots of generics (error messages can be quite something!), and keeping track of source code spans (where did the `LetItem` come from) can be a bit of a pain, whereas Tree-Sitter does that automatically.