Been reading that stuff a bit and indeed it's interesting! In the end there are several factors affecting TSH levels making it very unreliable to measure the wellbeing of one.
From somewhere else I read that it's mistakenly considered the golden standard because it's one of those things you can measure that accurately so it has lead to false idea of it being good marker of thyroid status.
And as we know it tells how hypothalamus pituitary axis is functioning. If one's brain is satisfied with less T3 their TSH would never rise very high as the demand of brain tissue was achieved with less effort leaving the rest of the body very deficient?
And if in some cases high TSH causes swelling of pituitary wouldn't that compromise the function of pituitary same way than tumour and could result in similar situation than in secondary where other hormones could be compromised too? So that would partially explain low cortisol which would then bounce back when TSH is lowered as swelling of pituitary would reduce as well.
Lots of ifs and buts!