I think the only way for B4B to work is if they adjust the skill. So maybe 15% damage 15% taken so it's literal blood for blood lol.
Doing so would mean that B4B and Darkside with FoF would be on par damage wise.

You do have cooldowns you can use to cover the damage taken. You guys are also forgetting that Soul eater and Bloodbath can get your hp back with the more damage you deal.

The real issue here is getting a provoke if we change DRK to MRD/LNC.