Obviously since we're talking about a collaborative interactive medium then the Darkness and lack thereof becomes a matter of how the Storyteller and their players approach the setting and system. I'm a Forever ST and I'm flexible on the precise tone and themes depending on what my players prefer albeit doing my best to respect the writers/artists of the splat. It's a bit murky to actually rank the gamelines in terms of darker/less dark because what actually is more upsetting/violent/wicked is somewhat subjective. I could make an argument for any one being the "darkest." I'm especially willing since it'd let me ramble for hours about media criticism, especially my studies of Gothic horror, urban fantasy, and variations thereupon.
Darkness is more of an absence, distortion, and deprivation of qualities than an actual substance we can scrutinize. When we talk about Vampire: the Masquerade being dark we're usually not talking about the fact that it mostly is set after sunset and before sunrise. The Kindred existence is dark because vampires are obligated to deceive, thieve, and otherwise violate people to survive, they must participate in even worse systems of deceitful coercion and desecration in order to stay on the good side of vampires even more powerful than them, and even disregarding both of the above factors, Kindred are dead, everything human about them is a corpse only partially engaging in life, there are pieces missing and at-risk of falling away.
This applies to the other splats as well. The key here is that all splats have people who exist in a world where their personhood is ignored, deprived, or even denied. The Supernatural exists as being negated by their circumstances. If the world did understand, provide, and accommodate their personhood then the Gothic-punk element would be severely blunted. The peoples-in-question participate in their own alienation both out of necessities, their own unwillingness to accept the personhood of others, and other contextual/experiential deficits. Nonetheless, there's an underlying sociocultural commentary for every game, just with supernatural archetypes. Our like/dislike of certain splats over others is often rooted in affinity/disillusion with the specific themes and tone.
Changeling: the Dreaming is perhaps the best example of this tendency, even though I'll freely admit to other flaws barring its critical/popular success. Changeling's tone and worldbuilding is not that different from the other splats. The players are still marginalized beings, the odds stacked against them, and they're asked to maintain their sense-of-self in a world that doesn't know their truth, doesn't provide them with help, and refuses to respect them as people. The main differences are the precise nature of what it means to be a part of the Fair Folk, how Changeling society is organized, and what the players do to affirm their personhood. White Wolf designs with highly narrativist gameplay in mind, character and plot above all. Chronicles are based on immersing the player more in experiences than realities.
To be a Changeling is to experience the world that has abandoned toleration of mental and emotional uniqueness. In the same way Werewolves experience a world that is apathetic towards its own decay, corruption, and death, Changelings endure a world apathetic towards its own boredom, calculation, and conformity. The horror of the Apocalypse is drawn from the horror of profit-seeking and hatred of nature; the horror of the Dreaming is drawn from the horror of medicalization and hatred of abnormality. What is worse? To be hunted as the enemy of the political status quo or to be treated as the enemy of the social status quo? Changelings fight for the opportunities to continue expressing themselves with sincerity.
In the same way W:tA wears its environmentalism/anti-colonialism on its face, C:tD wears its neurodiversity/anti-psychologism. Is it subtle? No. Is it advisable from a media-critical perspective? That's debatable. My point here isn't to force anyone to like/dislike anything. Quite the opposite, I encourage people to seek out what appeals to them. However, to tell newcomers that C:tD "annoying", "cringe", or "too bright" is almost a guerrilla commentary on what White Wolf clearly intended. Again, I'm not begrudging anyone their opinions and I could make the case that Changeling: the Lost might be better suited for its conceit but I've run C:tD for several years, I've made lifelong friends through it, and I look back fondly on it even compared to the other gamelines I love.
Take it with a grain of salt because I'm just one woman who loves tabletop:
C:tD is just as edgy, moody, intriguing, sophisticated, and engaging as the other gamelines. It's not without flaws but it's not without the aspects that make other segments of the oWoD excellent.
