At least this admits a lack of scientific knowledge on the subject. And it acknowledges the individuality of patients which would discourage a one-fits-all approach. Much work still has to be done.
"Lastly, substitution therapy may be complicated by interindividual variations of deiodination. The question, if monotherapy with T4 or a combination of T4 and T3 should be preferred, is for years subject of debate. Numerous trials [413–422] did not lead to a standard recommendation. Persons with abnormal sum activity of deiodinases, however, might benefit from additional treatment with liothyronine[414, 423], although this does not hold true for all polymorphisms of deiodinases [424]. Calculating GD or T3/T4 ratio might help to stratify patients for an individualised therapy, but the required trials are still to be designed."
academia.edu/18145143/TSH_a...
Just noticed that professor Dietrich is a medical advisor of Thyroid UK. So this might have been posted before.