Either way, in your scenario what you're saying is that the population of people susceptible to hypothyroidism is the same across elite athletes and non-elite athletes, BUT the training of elite athletes is so intense that it causes them to seek treatment in significantly higher numbers than non-elite athletes.
I would reject that...though I think it maybe the 3rd (could be 4th most likely scenario).
Consider this: Instances of hypothyroidism is less than 1 out of every 20 people in the general population. At a stretch, maybe your could justify that this number could increase to 1.5 / 2 out 20 if everyone in the population trained to their maximum. (Remember, most elite athletes don't have this condition...so we couldn' argue that this number would skyrocket to 10 out 20 - there's no evidence to support that).
Given that ratio, what is the likelihood that a 9-time American olympic gold medalist, a stripped american Tour de France winner, the first American olympic medalist in the 10k in 50 years, the fastest American born marathoner ever, etc...all are susceptible to hypothyroidism under extreme training conditions?
In my opinion, the answer is that the probability is not very high (but, okay, that list wasn't very scientific...you get my point. I don't have the capacity right now to do the necessary research).
I'm still in the camp that athletes using drug are most likely cheating, and the value add of this drug is simply to correct the chemical imbalances caused by the cheating. (These body building threads seem to support exactly that. Or, if nothing more, those thread would indicate that the drug is used for weightloss, which is also cheating).
When you reject that elites have higher thyroid problems for legit reasons I think our are missing another scenario and that is... given the same thyroid levels an elite may see performance worsen where a non elite, more sedentary person would never have noticed the issue and therefore not been diagnosed. This would explain why is appears that a higher percentage of elites have thyroid level issues than the general population.