Agreed, but we know this from a reader's perspective, not an in-world one. Jasnah and Dalinar are most likely unaware as to how broken and insane the Fused are, and have no idea they really only need to hold out for a few generations. Plus, we had the vision of Honor telling Dalinar that a contest of champions is the best path to victory, that's not something Dalinar is just going to ignore. Add in Hoid's approval of the plan, and it makes sense why they would see it as a viable option.