Let me get this out of the way first:
@tsumugi, and I are both going (or have gone) fiend. This doesn’t mean fiend is the best, it just means the sets are close and fiend better fits our circumstances.
@Lais You have 2 fiend, you should probably go fiend, the difference isn’t nearly enough to split your monos between 2 sets this early.
That being said If I had to hazard a guess I’d say that chart was made using civs rather than heblon, in which case the 54 ele damage favors fiend.
Even if that isn’t the case, using a baseline amount of int (3k for both sets) will favor fiend over gespenst, as part of gespenst’s value is an extra ~200 something int from raw stats/armor bonus over the other sets.
This is why under “mock sader scaling” (5k extra int) venator begins to outscale gespenst.
Also note that like @tsumugi said:
I use an average of all the skills, wherein gespenst is heavily weighted on its 1a/2a.
tl;dr shit’s complex.
Also crow is really heavily weighted on its 5set bonus, going 2 gesp for damage is probably bad.