Prestige matters in finance, too. However, a JD's not really comparable to an MBA because (a) getting the post-MBA jobs you mentioned typically require prior, relevant, gold-plated work experience (Switching into these finance sub-fields is VERY hard even for HBS MBAs.) and (b) these jobs don't require an MBA (unlike many jurisdictions that require accredited JDs). JDs typically don't have gold-plated work experience and have to rely on their law school's brand for signalling.

In other words, most HBS folks who choose this high finance route already have the credentials and pedigree for the job without needing an MBA.

For the rest, I recommend googling HBS job reports and re-thinking a few of your assumptions about where/how people create value at firms.