Source please. And this has nothing to do with Obi being superior to Vader.
ANH AC. It says why he didn't kill Vader when he had the chance, so it does have something to do with it.
Look at that comic. They're 8 Jedi, Not all of them attack him at once. The First jedi who attacks him sucks and is as stupid as TPM Anakin, so, naturally, she gets pwnd. Next Vader fights two okay Jedi at once, pushes a third back with ease. Then he fights one pretty strong Jedi one on one (what the hell were the others doing?). That one Jedi manages to disarm Vader before getting extremely overconfident and also she doesn't know that Vader's really strong even without a blade, so he picks her up and snaps her neck. There goes two Jedi. Next just 3 of the 6 Jedi attack Vader while the other 3 stand there and watch. Vader kills one of them, then the five remaining Jedi fight him at once and he loses. Then he pretends to surrender and some cocky bastard Jedi kills Bultar Swan (4 Jedi left), attacks Vader and dies due to extreme overconfidence. Then they're's only 3 left and they beat Vader, he has to get his ass saved by Clones.
So really, it's not that great of an acclompishment, the only time he kills Jedi is when they're really overconfident or when they don't all attack him at once. When Vader fights five of them at once he loses, plus the three strongest of the 8 get killed not by Vader, but by Clones.
Apparently, they were all Jedi masters too.
Says who/what? The first one he killed had a braid.