That's not turnstile, that's a Managed Challenge.
Turnstile is the in-page captcha option, which you're right, does affect page load. But they force a defer on the loading of that JS as best they can.
Also, turnstile is a Proof of Work check, and is meant to slow down & verify would-be attack vectors. Turnstile should only be used on things like Login, email change, "place order", etc.