The idea of a generalist leader comes from the French military in the early 17th century. Specifically, the concept of a "General" meant that you have enough broad experience that you could reason about the whole of a service component and be fungible with other "General" officers.
You can think of this in contrast to the "Specialist", which is an entry level job, meant to focus on one very narrow non-fungible technical task, with no ability to transfer to do other things
When this system arose, there weren't that many different things you could do in an Army so it was possible to actually be pretty useful irrespective of where you were and the biggest determinants were most likely IQ or something similar.
My experience with General Officers today however indicates to me that this is no longer possible --- more likely it was probably was never really true and there are a lot of examples in history where this was true.
I doubt you could put the CEO of John Deere in charge of Merck and expect that things would continue to run as effectively, or as efficiently.
It's pretty silly to me as someone who has been in management/leadership roles since 2008 that people think leadership is fungible and technical skills don't matter. Trust your gut and it will be obvious that this isn't true.