It's not just tree-sitter that makes zed feel snappy.

If you're using a reasonably fast language-server, which rust-analyzer apparently is (I didn't know this using vscode), the autocomplete & intentions feel instantaneous.

I think the team has learned a lot from previous editor implementations (they were the core team of atom that was notoriously slow), and so they've had an opportunity to do a lot of stuff right.

FWIW they also are the team that originally wrote tree-sitter.

The quickness feels more like it's in the core of the editor. I was shocked how much it impacted the editing experience when I tried it in early beta.