yep i have the same problems .
i started my first mp game 2 days ago so i am at turn 2 = no expierience in mp
i liked pyhthium but as you say there are no good astral summons . and i don't know yet how do design a good pretender for pyhtium because the arch theurgs are expensive and the principles need much resources so you can't take a sloth scale .
if you don't have some paths at your pretender you have nothing good to summon
in the late game with astral 3 water 1 on arch theurgs you only need +1 water / astral and can summon abominations but thats really late game .
blood is only useful if you find indep blood hunters and/or a site with a high blood summon bonus of 40+% ihmo .
i really like pythium but suck with them