How to know if a job makes a difference

Agree. I thought the leverage one was the odd one out - more ego than impact. I think high impact organizations are usually made out of individually low leverage people working together

Maybe it's more like recycling.

Overall, there's probably a net positive in recycling in awareness alone, regardless of how much "recycled" material just goes to landfills.

And it's a way to signal socially to find like-minded people for a "safe" work environment. Instead of trying to avoid "toxic" workplaces, it's some kind of positive attribute to seek out.

In an odd twist of faith, the person(Fritz Haber) who’s method is used to get fertilizer, is also invented zyklon b and was used to have a different type of impact.

Depends how you define "big impact". If you influence conversion rate for a product that earns €100 mil per year by 1% you would have impact size of €1 mil/year, which if you made it yourself could impact the World in any number of ways you wanted. €1 mil per year impact is at least to me quite big.