Wejo I believe that what really happened (apart from the rain and wind that some claim and surely have affected the outcome) is that during the last 8 years Bolt has made us believe that a 19:50 or under is the norm.
The reality is that a sub 20 200m is an amazing time, Bolt is long past his peak and still could crank 19:78 twice during these championships.
People expect to see 19 low when bolt is running but if you remove him from the last 8 years the best times are from Blake, Walter Dix and Gatlin (19:26 , 19:52 and 19:59) that's it. These are times that should be a LOCK for a gold anytime before 2008. And probably with a big margin too.
Cheers.