I generally agree with you on that, but my partner started a new job (as a technical lead for an engineering team) about 6 months ago, and her onboarding was actually pretty good -- not perfect, there were some snags, but the overall experience was positive. Was it as good as in-person onboarding? Maybe not as good as if she were in-person at this same company, but IMO it was still better than the in-person onboarding I've seen at other companies. She started getting solidly productive after two months or so, which I think is comparable to most in-person jobs, especially when you're not joining in a more junior position. But social connections with the members of her team were definitely slower to form, and I think there are still (after 6 months) some holes there.

But... that's kinda ok? A company might be upset at any negative effects that might have, but I personally think it's a completely acceptable (fantastic, even) trade off for the ability to eliminate a commute, work in comfort, and have a more flexible schedule.

Obviously not all companies are going to do remote onboarding well. Just as many companies don't do a great job of in-person onboarding either. But that doesn't mean throw up your hands, give up, and make people go back to the office. It means... do better.

I do think remote onboarding is especially hard for people starting their first job in the industry. But I'm not convinced these problems don't have solutions. Maybe not perfect solutions, but good-enough solutions.