Interesting, IME it's all beans. At my go-to place, the baristas are pretty bad but the two owners are super dedicated to roasting their own beans, you can always see them putting a lot of time and effort into it. Result is much better than places where the baristas are skilled but they use cheap pre-roasted bulk beans.

To take it to an extreme, I doubt the best barista in the world is going to get a good shot out of the default Starbucks beans. But maybe I'm wrong!

You're not wrong, bad beans are bad beans. But on the other hand, no matter how fancy single origin perfectly roasted beans you have, a crappy barista will most likely pull a terrible shot.

Beans can't compensate for the lack of skill.