No, but they can adjust much quicker than regular employees. Adapting to new environments is a skill that can be trained. Freelancers who do a lot of different jobs for different companies have a lot of training.

But you are missing the point. The idea is to have a small core of highly skilled devs who can chop complex tasks/systems into bite sized chunks that can be outsourced.

I've seen it work, but it's very difficult to pull off. I've seen it fail more often.

According to the job ads that need someone to "hit the ground running" they do.

As a dev employee turned freelancer, the onboarding is still there but much different. Much more focused on learning just enough to work on specific tasks vs poking around for a week or two and figuring out the whole system. I'd say I spend 1/4 the time onboarding as a contractor vs as an employee.

With freelancers you can just stop paying them after day 1 if they don't and try another. In some verticals of software development there is a ton of supply.