If it's really trivial as you say, Google's reCAPTCHA and similar products like hCAPTCHA would instantly have no reason to exist.

Bot intentionally trying to look human =! Spider

A spider will generally have a pretty predictable route through a web site.

The various CAPTCHA implementations are primarily designed to prevent bot submissions, not spiders.

Some of them yes. But not all. Try for example to browse a Cloudflare protected site from Tor and you will be hit with a constant barrage of captchas even though you are only doing GET requests.

Yes, huristicly, a tor browser is more likely to be nefarious than a regular browser user. Note the use of huristisc - such as IP address - not related to user agent.