This article seems to define a polymath as someone who is an expert in one domain and has opinions in other domains - those opinions being given greater value because of their other expertise. However - I'd argue that a polymath is someone with expertise in multiple domains. And the real value of the generalist is the ability to join the dots between specialties. We can argue if polymaths exist - or who might be one - but I think the definition stands. My background is medicine and I've seen first and the different contributions that generalists make vs specialists.
I think casual polymath seems like the wrong descriptor to use - as they're not experts in other fields.
They're experts in one field, and (most probably) dilettantes in other fields.
The trick however, is that they use their expert status from one field, to reach their audience. And then their followers will take that as domain authority, because they're perceived as authority in some other field.
I'm not going to name names, but this certainly fits the pattern of a lot of people in the VC-industry. Not that they brand themselves as experts (sometimes they'll explicitly state that they're not experts) - but their followers will assume that it's expert knowledge.
I come from a science background and have similar experience. It really reminds me of the adage "if all you have is a hammer, everything looks like a nail".
One thing I have found is that while not all generalist suggestions are good, they can at least provoke the specialists to think about the problem differently.
