Yeah, that is weird, but readers are sometimes dumb. Though, I would say being one-note is bad, too. I like having dark sprinkles in my light stories. Occasionally, they will touch on hard topics, but they don't go too deep into them. Nor do they linger on them. It helps to break up comedy and SoL with a little of it, IMO.
It kinda got a point though, going too far is bad sometimes. (but can easily be solved if doing a small note in sypnopsis like CNs like : "Very heavy dark plot" or something. Or "No heroine")
Agreeing with Envy. Sometimes spicing things is nice.
But a particular problem that i hate (immerhate activated) : is all this shitty novels that say they are "fluffy" "heartwarming" but its bs and/or full of drama.
To cite an example, when i was still using NU.
I tried a shoujo-ish CN. Tagged heartwarming, 2 reviews saying its sweet.
The FMC is chased by 5+ guys. Her life is shit and bullied (and people wanting to rape or kill her).
The ML was chased by 6+ girls toxicly. Like the retarded roommate of FMC that think he wants her, despite FMC more pretty, and he clearly focus-talk on FMC, when both present.