I reported this in 2.1, and it hasn’t been fixed yet. I think I saw a dev (maybe Sirrian) say they were looking at timing for 2.2, since it would require a decent amount of code rewriting.
Hilariously, Lyya, Dwarven Slayer DOES overcome life drain, tested against a Vampire Lord. So either the problem is specific to Wight, or it’s specific to Bombot. It doesn’t seem to be a generic timing issue.