You rank a full season based on a number of factors.
First, you heavily weight the championship race. Centro gets the most points here.
Next, you heavily weight the seasonal best performance. Centro was #21 on the world list, pretty weak.
Then, you give a lot of weight to consistently running well in a series of races. Centro did crap here. Didn't even run Pre.
You also give credit for running a number of top performances on the world list. Centro scores a zero here.
He ranks #1 in the Olympic final, not on the year as a whole.
I've never seen an athlete that was the number 21 performer get a number one ranking.
Add zero Diamond a League wins to that.
Again. To say the Olympic Champ automatically ranks one is to say you will give no thought to the rankings.
(Considering indoors and USATF into consideration artificially inflates rankings because the competition is not there. Indoors gets a separate ranking anyway).