The uptime of the black heart is something like 10%, so when it's up it's REALLY ridiculously good, the problem is it's not up that often and you're kinda floating things to the RNG gods. To an extent you can make those average armor calculations, but you have to weigh the fact that the buff won't be up and you're not getting a constant ~1k armor. The Glyph of Indom is constant and is more EHP than the black heart.
Run with the skeleton key and glyph of indominability imo.
"If the world is something you accept rather than interpret, then you're susceptible to the influence of charismatic idiots." -Neil deGrasee Tyson
Twitter @Aggathon || @Tankspot || Twitch.Tv/Aggathon