Not sure what one can glean from one battle, where one character was shorthanded and there was a decent wild card character in Hermit Yoda involved. One G12 against 3 G8 -G9 characters is not an autowin for many G12 characters.
Especially if there synergy's involved.
Plus i am not sure where you get the idea that Vader is a Jedi killing Machine. He was know for being a top pilot, strong in force and master tactician. He did not kill many Jedi's if any except for Kenobi when he laid down his saber.