That's actually exactly how it works. Endeavor is a company owned by Delta and run by a Delta employee. The Endeavor corporate ladder does not extend above JG.

Are LATAM pilots Delta employees? How about Virgin Atlantic pilots? Those pilots work for Delta subsidiaries, too.

Under your logic, a Virgin Atlantic pilot would be at least partially a Delta pilot. The whole point of Delta owning part of Virgin Atlantic is that a Virgin Atlantic pilot is 100% not a Delta pilot. That same logic applies to Endeavor and its pilots.