If you're using both the degree and the bootcamp to achieve the same goal (e.g. a paying job), then surely being ready for employment sooner is preferable?

No. I can get a paying job right out of high school, while someone going to medical school will be hundreds of thousands of dollars in debt for over a decade. If you are just looking at wealth at age 25, people working in fast food made better choices than doctors. Yet somehow, 10 years later, the doctors are ahead.

Clearly that is an extreme example, but it illustrates the point - getting a paying job quickly does not mean it is the best answer for long-term salary and career growth. Getting any old coding job just to get one is not the same thing as getting the full education that comes from a degree. That doesn't make it the wrong answer... getting a job matters. But if you are comparing long-term outcomes, you need to look at it with more context.

The analogy doesn't scale because additional years of fast-food work don't add anything to your prospects. On the other hand, additional years of software development add a lot to your employability so the value of getting your first job is much higher. Once you have several years of experience, the lack of a 4-year degree is far less harmful to your employability.

You can think in terms of ROI only if you have enough resources to dedicate 48 months to study. Otherwise it's just a race against time to become profitable.

That is, to be able to think in terms of ROI is a privilege.