fritz:
sfo:
MKW:

those bumps are just wrong

I assume that that's a car specced for the USA market. Porsche used to have to add similar bumpers to the rear ends of 911s to enable compliance with a test (referred to as the "pole test?"Smiley) imposed by the US car insurance industry. 

991s have no such bumps, you would expect the AMG GT (newer than 991) to have addressed this issue