Has anyone pointed out that "BrainsTrust" (in the UK at least) is mostly used sarcastically to mean a stupid/idiotic person. So I think you are onto something here.
Yes, not saying it's never used ironically - I agree that that is probably most common - just pointing out that it originated as a serious label for anyone unfamiliar with the history.
FWIW I'm a UK resident and have never heard it used sarcastically.
As another UK resident, I hear it used sarcastically frequently.
I've only ever heard it sarcastically here in Australia.
All have anecdotal evidence. All must be right.
That is all.
In the US it is often used with a positive connotation.
Connotation or denotation is all in the intonation, which is hard to hear in textual form.