I want to back off from 'All the good ideas have turned out to be simple', I think that was a rhetorical flourish too far, and I think you were right to call bullshit.

I bet there are good ideas that aren't that simple, like e.g. the monster group or quantum chromodynamics. Neither of which I understand well enough to see whether they're actually simple, or inherently complex. But either way, it seems unlikely that the degree of complexity that fits happily in a human mind is also a limit on the complexity of ideas used in the construction of the world.

But I also want to defend: 'these symptoms are caused by deficiency of, or insensitivity to, thyroid hormones'

As a really simple idea that makes lots of predictions about real experiments that can be done.

Do you really think it isn't, or are we just arguing about 'All the good ideas have turned out to be simple'? If the latter, then you win. You were right and I was wrong. Thank you for the lesson!