It's not totally random, but yes, it is heavily random. This is why the
old great demons were done by saccing tons and tons and tons and tons of
items, to find the perfect random. Sure, the sac values were different
back then, but still. I think Baltzebub alone sacced easily hundreds of
xormors in addition to the large amount of real eq saccing. Now, for the
really top demons you do need huge sac values, and with ridiculous sac
you get ridiculous demons (like the 25m sac sbs, demon was dested after).

Now, as the current guild maintainer I'll share this. I'm pretty happy
with the random, making totally awesome demons shouldn't be simple, and
lets face it, there aren't that many totally yber sac-items around,
just making a good demon from every great sac would go against the design.
Now, I know the sac values of many many items have been lowered, so
the sac formulas could perhaps use with some re-evaluating. However,
looking at the code makes one despair, so I wouldn't keep my hopes
up. It works, so I'm not going to try to fix it...

-Era of slacking