I have a lot of strong feelings on this subject, and a great deal of it admittedly hypocritical. Especially so when I'm going off a combination of extremely hazy recollections of watching Sailor Moon reruns as a very very small child, and an extremely loose understanding of the current anime industry filtered by popularity rather than seeing the whole of what's out there. That being said...
Again, I watched (the english dub of) Sailor Moon on TV as a kid. I don't remember much from it frankly, and if I had the time and money I would love to just sit down and binge it all again. What I do recall is a general impression that in the end, even some pretty nasty situations worked out, and Usagi and her friends were the ones to make it happen. Pretty basic, maybe, but it meant a lot to me. Most of the other stuff I saw at the time was uh... simply sexist, and I was on the timid side myself. I thought it was cool that these girls were the heroes, not just a frequently-helpless token on the fringes of a male-dominated cast, and it was something I looked up to (Even during a decade plus of being entirely detached from anything else to do with the genre, until rediscovering it and what had become of it fairly recently.) As others have pointed out, SM was apparently not berefit of darker elements, (even if my recollection isn't as reliable on that front, though some of that is possibly due to differences in presentation rather than content compared against modern series) but the throughline was ultimately optimistic and empowering.
And so that's what I look for.
I don't necessarily think tackling darker or more adult themes is a bad thing. In fact, it can be a good one, if done well. People would talk down to me for being a child, and people sometimes still talk down to me because I'm a girl. Even if well-intentioned, trying to dumb down a conflict like that just feels patronizing to me, so I hate the suggestion that there should be nothing heavier ever and it should all be a cavlacade of oversimplified happiness. The issue is more in presentation, intention, and agency. Especially agency. Is the presentation hyper-detailed and gory for shock value, or more tasteful? Are these darker elements present because they are being legitimately explored and discussed, or just because the series wants to look cool? And are the characters actually heroes doing something to improve the world even if it comes at a personal cost, or are they also helpless, with their efforts rendered moot and their hardships in vain?
It's not about whether it's dark. It's about whether it's nilhistic.
I will say that more classical series have had some uncomfortable tropes that Puella Magi Madoka Magica called out, particularly with Kyubey and his contracting. Regardless, I do hate how it's essentially resulted in an attitude where the mere idea of becoming a Magical Girl (a girl becoming a hero) is treated with suspicion and expecting a catch or drawback beyond the basic responsibility such a position entails, because clearly the mascot has to have some sort of ulterior motive and the girl is just another helpless pawn. This is the nilhism that's crept in that bothers me.
Some series seem to be better about it than others, but the two main ones I've had the chance to watch (Madoka itself, and Yuki Yuna) both take an approach of trying to have their cake and eat it too, with the drawbacks and the deconstruction, but then a hasty happy ending to offset that. (Madoka at least gets a pass because rewriting the setting mechanics to make it possible is the entire point, but Yuki Yuna was much sloppier about the whole thing in a way that makes me suspect the apparent optimism there was forced and insincere, especially after the big twist of a few episodes earlier.) Other series, like Raising Project and Site, sound like they don't even try that much. So what I see from those is a pretty persistent theme of "everything is out to get you, you are helpless, everything is pointless, and only if you're extremely lucky a literal miracle might come along to make things better." Very different from the takeaway I got from Sailor Moon as a child.
And again, this is only a small corner of the totality of the Magical Girl series out there, and it sounds like the vast majority of them do retain that core of optimism that I consider so important. Unfortunately, it's also the loudest corner now, with a lot of the rest requiring much deeper digging to find. The online culture around magical girls has similarly shifted, with the default assumption being the revised expectations Madoka has set forth. Sometimes that can be handled well, but much like the official products, much more often it seems to lean into that for shock value and being dark for darkness' sake rather than saying anything meaningful with it.
