If you want a grim & gritty system, where lethality is high... go with VP/WP. Heroism is irrelevant, luck rules all.
It is utterly the wrong fit for D&D. If you want a high-level character to be threatened by a low-level character, you lose the opportunity for heroism. It's a system that wprks against the main strength of D&D: that combat is fun. Combat where you die every four encounters is not fun.
The threat of death does have to be there, and it is in D&D, but it's death because you pushed too far, not because some commoner rolled a 20.