There seems to be a gap in the storytelling. I got the impression that Venat did work with the Council of 14 and did her best to convince them that summoning a blood god was probably not the smartest course of action, but she's fighting against the egos and naive worldviews of people like Hermes and Emet-Selch, who also think they know best.
She even said that she wanted Hermes on the Council in the role of Fandanial, because she felt that having "the best minds" approach the problem might find other solutions.
For a people whose every solution has been "fix it with creation magic" to have that suddenly not be an option was incomprehensible to them. They couldn't let it go. Plan 1A was summon a god so powerful it would stop Meteion, even if it cost them half their souls. Plan 1B was to have a bunch of children, and then sacrifice them, to bring back the first batch of lost souls. Neither facet of that plan solved the real problem, which was stopping something that couldn't be stopped with creation magic.
Were there likely some outside of the box solutions that the Council should have explored? Yes. But that would entail them believing crazy old Venat's story: that a time traveler from the future came and told them that their world was going to be destroyed by a non-aetherial based creation.
Who would believe her?