Agreed on RCTs being the gold standard, the top tier of the evidence hierarchy (other than reviews of multiple RCTs).
However, if you choose a biased (corrupted) indicator, all your perfect measurement methodology can only minimize additional biases. A top of the line flood-proof house that you erect on top of a swamp will still go down. (Substitute with weakest-link analogy of your choice.)
Agreed on RCTs being the gold standard, the top tier of the evidence hierarchy (other than reviews of multiple RCTs).
However, if you choose a biased (corrupted) indicator, all your perfect measurement methodology can only minimize additional biases. A top of the line flood-proof house that you erect on top of a swamp will still go down. (Substitute with weakest-link analogy of your choice.)