I mostly look at recent world/continental results and world rankings for some sports while taking into consideration the qualification process. Naturally some sports will be more strict than others, based on the data that I have. In terms of wrestling I too was surprised that Iran didn't have an athlete in each male event, I guess they had (relatively) poor recent showings, I have no issue with adding them all, I was mostly waiting to see your reaction
I agree in basketball that China is the favourite, but with other nations competing things could get quite messy in the rankings.
For sailing, it more has to do with the weakness of Asia in Men's Finn. Iran's sailor (Ahmad Ahmadi) was third among Asian nations at the 2018 Worlds and one of those nations was Japan who is already qualified, the other is from Hong Kong. Of course, I suspect China will show up at the continental qualifier and take the quota, but if they don't I suspect Hong Kong and Iran will fight for that quota.