Absolutely not. While a captcha can stop somebody with a simple python script and nothing else. It is not effective against sophisticated bots which either use AI or which connect through API to a captcha solving service run by humans. Much to the chagrin of captcha operators.

From what I've seen the main purpose of captcha is to act as security theater to dissuade normies. If there's anything that captcha has been successful at it's been permeating pop culture as a trope. As far as actually stopping the malicious actors it hasn't really done that much, mainly because these people will adapt and change their tactics. They're not just going to keep trying the same methods that aren't working, they're not stupid. Many do it as a business.