I agree the Jedi should use lightsabers more sparingly. Although, the “defense only” thing is hard to salvage even with the OT alone, given that Kenobi was supposed to be a war-time General. Even in A New Hope, Kenobi violently murders those two alien thugs in the Cantina. It was self-defense, obviously, but Kenobi could have handled them in some non-lethal manner, presumably. I mean, he could have tried to “mind trick” them into leaving Luke alone, for example.
To play devil’s advocate, we don’t know from screen evidence alone that Ben killed either of them. We only see a severed limb. It’s only the screenplay and novelization which have them mortally wounded, IIRC.