I agree with an earlier poster that mad scientists are frequently autodidactic. And obsessive. Having them obsess over any field would really sell them, though at least part of their study ought to involve math either directly or indirectly (like physics).

Really though, it seems that the mad science angle is always used for fields that are newish and growing relatively quickly in complexity. And in the modern age, groundbreaking work isn't usually done by a single person so much as it is done by teams of researchers.

So, I think it's the mad financier is the modern iteration of mad science. John Hammond, for example. They set the goals and organize the team, then reap the rewards. Since they do not even need to understand the underlying science, it's much easier for them to fall to their hubris. So they might even be better at the core story trope of the classical mad scientist.