Not all etymologies are lies, words do have origins.
Just because you heard some stories which were false doesn’t mean all stories are false.
On this wiki page it is explained that linguistics do believe the word Yankee comes from Jan Kees or Jan Kaas. It explains it can also come from the name Janneke, which is a new to me.
From what I’ve seen, they don’t even learn about the law and often break the law by illegal detainment, searches and confiscation. Cops who served for over 20 years but don’t know people their rights. They often get minimal training while having to serve alone where everyone carries a gun. That’s asking for problems. And now cops in the US are militarized with heavy combat gear, while the majority is white and racist. So obesity is the least of the problems with US police.