You dont have to, you can do a left power attack while standing i believe. Either way it seems simple to me. As for eating the corpse, u can just howl immediatley afterwards and it will automatically absorb all the health but cut the animation short. Instant heal. Worsecase scenario, u miss the lunge and do it again. And u can do it over and over and over as much as u want. Thats extremely reliable.
That's the problem, however. As soon as you stand still to do a power attack, you're exposing yourself. As for the lunge attack, after a while, it simply would NOT work properly. I would hold down the right trigger and literally nothing would happen. That's killed me quite a few times. There's no debating that werewolves do more damage than vampires, but vampires have much better survivability. I would go into large bandit camps as a werewolf, summon a few up, one shot a decent number of enemies, and then promptly get killed by some archer. With the vampire lord, that has never really been a problem.