Is job-shadowing a better, or adequate alternative to internships?

Shadowing is better than nothing, but I wouldn't shadow for too long. With shadowing, you're just watching someone else do their work, rather than doing work yourself. Yes, it's helpful in the sense that you get an opportunity to observe someone else in action, and you can definitely get a feel for their line of work, but shadowing is not particularly useful on your resume. Internships allow you to actually do work that leads to accomplishments that you can put on your resume. Employers care more about "what you accomplished" than "what you witnessed". I tell my students that the pecking order is as follows:

-Full-time work
-Part-time work
-Paid internship
-Unpaid internship
-Volunteering
-Shadowing
-Nothing

You want to move up the pecking order as much as possible.

What line of work are you considering, long-term? That might change things somewhat.

I like the job shadowing approach because you typically get a chance to see the ins and out of a company's process while gaining knowledge that you might not get with an internship. You also might get firsthand knowledge of any potential job openings before they go public.

Build a name for yourself and you might be able to get your foot in the door before a job is announced.

I tend to look at internships (especially the unpaid kind) as the busy work person. The person that just gets all the work dumped on them that no one else wants to do.

At least when you're shadowing someone, in my opinion, you could be learning something that is actually useful for what you are trying to accomplish.

Sounds like a great approach but the concept out there is "you get what you pay for" with an unpaid internship, so even seeking compensation under those circumstances may be a better idea. My two cents.