About Worldbuilding? This question asks if building a trans-Pacific ship is feasible using only merchants as the shipbuilders. (They die horribly in one way or another.)
Off topic? Nope.
Idea Generation Not IG since the question asks for a binary Yes/No with some justification. IG tends to generate open ended lists.
What good are herbivores in an animal army?
About Worldbuilding? Yes.
Off topic? No. A fantasy world of human style conflict but carried out by carnivores and herbivores is definitely worldbuilding.
Idea Generation No, since the question outlines a set of constraints for the answer.
How to defend against the “convince-me” ray gun?
About Worldbuilding? Yes. The question focuses on a world mechanic involving a semi-involuntary mind control/idea implantation at a distance.
Off topic? I don't think so. Mind control ray guns seems very world-builder-y to me.
Idea Generation No, because there were sufficient constraints to limit the answers and decide a "best" answer.
How do you find a mate when everyone looks amazing?
About Worldbuilding? Yes. The question asks for a description of specific adaptations or sociological systems that would influence how a person goes about finding a mate when personal appearance is no longer fixed.
Off topic? No. Genetic manipulation of appearance is definitely on topic.
Idea Generation Likely not. Though this question can generate a list of possible fitness criteria,
What is the best apex predator to thin the zombie herds?
About Worldbuilding? Yes. The question addresses natural ecosystems after most humans turn to zombies with respect to apex predators. Asking about the entire ecosystem would have been too broad.
Off topic? No. A world of zombies is definitely WB material.
Idea Generation Edgy. The question asks for "the best" apex predator to thin the zombie herds but doesn't really specify any criteria for what constitutes "best".