The vine ogres are good as well as the manikins and all blood 1-3 summons as well .
Only the vine ogre are from conjuration path . So imo you are right
.
I would even say that all the summoned units from conjuration are rather crappy . The commanders there are way better .
But for units always go blood if you can
. If you don't have blood take a look into enchantment and construction , living statues , mechanical men + mandragoras are all quite good .
From a cost viewpoint though devils + storm demons are probably not too beat .