I'm no good at SEDE. I doubt this will change. But I know, deep in my heart, that worldbuilding is by far the best Stack Exchange site.
So, let's crowdsource.
What are some statistics that prove WB.SE is the best Stack Exchange site?
There's a reason why it's good to avoid superlatives (best, worst, greatest, least...) when asking a question — they're always subjective.
Worldbuilding is fantastic. You will find no Stack with greater creativity, greater imagination, greater flexibility, etc., than on worldbuilding.SE. And we're the only Stack (I believe) with its own, dedicated god: Glarnak
And you won't find any of that by searching SEDE, which is only interested in network statistics. We're among the least populated stacks and therefore host among the least number of questions and answers. If we were top-ranked, it might be in negative things like number of questions closed as a percentage of questions asked or least-likely-to-upvote.
So, as with many of the questions asked here, it really depends on your perspective. Well, that and why you're asking. Why are you asking? Is there a pizza hanging in the balance or something? I'll flat-out invent a reason why we're the best if there's pizza at stake.
Worldbuilding stackexchange is certainly amongst the least toxic ones, I know the music, fitness, vegetarian, economy, anime, biology, medical and programming stacks.
Worldbuilding + Vegetarianism stack exchanges are the only non elitist ones I know.
I don't know about statistics but there's plently of youtube videos for young programmers suggesting to avoid stackoverflow due to it's toxicity and elitism and in my opinion, for good reason. I think the other stacks are similar.
But I don't see any youtube video saying worldbuilding.stackexchange is to be avoided.
In my experience, in terms of who's the least toxic and has the least elitism and gatekeeping, I would rank them as :
2nd Vegetarianism but it's dead now