When so much of my resume is NDA'd it really starts to feel like "I'm a great painter, I promise, I'm just not allowed to show you any art I've made"

100%.

On the other hand, open source culture is vastly different from proprietary culture.

So many times in proprietary culture I've churned out craptastic code to meet a deadline that didn't matter for a project whose customers were straw-persons. There's definitely some projects or features I've coded which I'm glad to hide from public view.

That said, artists can curate their portfolio, and unless they're presenting to a public forum, their turds won't have to see the light of day again.