I think that's any uniformed fan, it's not just relegated to the Red Sox and Yankees...but since those two teams are so high profile in the media, they're easy to point to and laugh at. These people don't spend hours on a site like this...they just listen to talk radio, they watch some games, they don't know much past that.
So they make those trades, their system is bare and the prospect they trade away goes on to play well somewhere else...they'll cry about that guy having success somewhere else, too.
Anyway, not surprised about Devers being bad at 3rd, all you had to do was look at that guys body type to know what his future would look like. Some bad-body athletes (Kirby Puckett comes to mind immediately) can still play despite carrying some extra weight around the middle...but those guys are usually exceptions, not the rules. Devers is barely 6 feet tall, I don't know if they'd want him at first base in the next few years.