An MBA, precisely because it is so broad, is a much better degree for someone who fundamentally doesn’t know what she wants to do than a JD. If you get a JD, or “just” a JD, chances are good you will be roped into practicing law, at least for a while, and if you don’t actually want to do that it will be excruciating.
By the way, many things that get said, perhaps with justification, about MBA or JD degrees in general, have little or no applicability to an MBA degree from a top-5 school, or a JD/MBA degree from one of the four schools in the top 5 where that’s possible. At that level, either degree (or both) is effectively a guarantee of full employment, unless your personal demons make full employment impossible.
Introvert vs. extrovert is not the issue. In the business world and in the law world alike, there are many, many successful introverts. What there may not be is many, many successful people with severe social anxiety. You have to be able to manage communication with other people and teamwork in either world. If you are not doing that successfully now, you should invest some of the tuition you are not paying in some serious therapy/coaching about it.
It has been true forever that most JD/MBAs are contemptuous of their business school classroom work. It’s not as intense as law school, even when it is intense. That said, relatively few of the JD/MBAs I know stayed in law for long. The degree that’s most valuable to them is the MBA. As others have said, though, the business world has plenty of “only” JDs who have flipped over to the business side.
My wife has a JD, and she hasn’t practiced law in 30 years. She finally let her bar membership lapse a decade ago, when she was running a $25 billion government agency. She is well-known in a field where no one has a law degree. But she would never tell you that her law degree is useless. She uses lawyer analytical skills constantly. (And when she was running the huge organization, the lawyers knew better than to try to push her around, as they often did to other agency heads.)