I don’t think there are studies. I learned this on a thyroid forum. It seems it t is a bit like diabetes, meds will tell you it is ok to be a lot higher in bg than it is.
Most people need to be at 1 or under to feel good. Everyone is different, like diabetes management etc.
People say you should go by how you feel not the numbers but tsh being too high is bad. In hashimototos if you don’t treat it eventually your thyroid gland will be destroyed. Your diabetes will be much worse to handle and you can have other organ damage. Your thyroid controls most of the organ systems.