For an n=1 I'll give my experience.
I did 4 years of wet-lab biochem research undergrad, then decided after I did my thesis I never wanted to touch another pipette. Halfwar through first year I started emailing around my resume to a few PIs in Gen Surg and Ortho who had published papers I thought were cool, and after making sure I was really sure that I didn't want to keep a basic science slant going (and offering first-author type projects for me to do on that front), they all had great projects for me to start on with varying degrees of autonomy. I wound up working with the one who gave me my own project from the start, then helped mentor me as my focus shifted from clinical research to public health, outcomes, and cost effectiveness work. When my career interests shifted, the new department I went to (Urology) had a number of attendings who were more than happy to tell me ideas and research questions they've had and set me loose. My research CV is a huge part of why I got interviews where I did (and no, I did not have an advanced degree coming in -- I came straight from undergrad).
tl;dr:
There's plenty of autonomy, first-author worthy work, etc available, but also plenty of support for you to learn and add to your skill set.