It's still irrational to me. The sundered are no more equipped to not become The Plenty, in fact, one of the notes states that they started out similar to the sundered. Venat may have kicked the can down the road, but it's not as if her 'solution' is permanent.

I hesitate to mention Allag or Garlemald because people get hung up on them being Ascian constructs, but Allag was close to "perfection" and Garlemald was close to the second world in the Dead Ends. It doesn't take a lot to manipulate mankind into destroying themselves.