im not sure how you cam to that conclusion but let me try and clarify.
What I am saying is that your body MUST get essential nutrients (ie vitamins and minerals) from sources outside the body. Thats why they are called essential. Failure to get these nutrients causes associated bodily functions to deteriorate over time.
Iodine and B12 are both essential, they must come from outside sources. your NEED iodine, you NEED B12. You can not get enough B12 (without supplementation) if you do not consume meat.
All of your bodies nutritional needs are based on many factors:
genetics: (ie gene defects etc alter how well or efficiently your body can make use and convert nutrients)
pathogens: (many pathogens actually target specific nutrients and/or enzymes preventing your body from being able to cenvert nutrients as needed. They also tax the immune system which adds additional nutrient requirements.)
Toxicity: ( many nutrients adhere to toxins and heavy metals which in turn get filtered out of the bidy by kidney/liver. Nutrients that suffer this fate are of no nutritional value to your body and are wasted in that sense).
My point is that we are all individuals we may have lower needs than most for some nutrients and higher needs than most for others.
You came to these forums and jumped on Iodine because you thought it was going to be the panacea of good health. Most people who have nutritional deficiencies that have manifested in poor health to the point of having multiple symptoms that affect day to day life are actually well beyond the point of having just a single deficiency and have graduated to having multiple deficiencies. A deficiency in just a single nutrient, if left unaddressed, can cause a cascade of other deficiencies over time.
Many of the B vitamins are crucial for proper energy metabolism. If you have addressed your thyroid nutritional deficiencies and are still suffering from symptoms that on the surface appear to still be thyroid related, my estimation is that your problems are bigger than just iodine.
You mentioned being a high carb vegan and at the same time complained if high cholesterol. High carb diets are known to increase cholesterol and vegans are known to very frequently have B12 and other methylation issues.
So, using some simple logic, you have been on high dose Iodine along with selenium and other cofactors for some time yet complain of problems. Its time to continue your search, take off your blinders and open your eyes to the possibility you have other deficiencies at play here. Many of the sides you are complaining about simply remind me of issues one may experience with B12 and methylation issues.