I've come to Mo Dao Zu Shi from a less-engaged fandom, so feedback has been a step up for me. But as for mainstream vs niche content--yeah. The numbers (hits, kudos) are lower for niche content, but the readers who do engage do so on a deeper level, and that's more satisfying than numbers. I'm still branching out in Mo Dao Zu Shi, so I haven't experienced that as much here, but in my previous fandom (Akatsuki no Yona) I poured my heart into a sci-fi AU that focused on the antagonists (and one character who hasn't even had an on-screen appearance in canon, so she's essentially an OC) and while readership was lower than for any of my other fics, I got some of the loveliest comments and even people messaging me to react to it in real time. It was nice.