It's only purpose is ultimate generation. If that is worthwhile to you then you can use it, but I honestly find light attacking more engaging and worthwhile than using this terrible channeled ability.
Edit: And yes I'm aware you can light attack before using the channel to get even more ultimate.
Reduce casttime to max. 1 sec. I would like to ce more 0.6 to 0.8 sec.
Scale its dmg much higher when on low life (max benefit at < 25% health, dmg should be spamable level atleast),
during the 1 sec duration u get a medium heal and a 10 sec hot after full duration, heal should scale of your stats, not your dmg done and the lower your health is.
Max heal benefit at 35% health.
That would synergies very well with the vamp spamable and frenzy.
It's the only reason why I don't use vamp in pvp anymore. Already cost intensive heals that heal for *** is even worse with vampire.