I would be somewhat surprised by your particular example (outside of a "bad" ending for the two), but I agree with your overall point.
Leah being a serial killer in AL (as opposed to a more mundane obsessive crush) isn't particularly well foreshadowed, and it completely dominates the last quarter of the game. The idea that something really bad couldn't pop out of the woodwork 3-4 episodes from now is just not consistent with how DPC has worked as a writer.
But can we really judge DPC on the basis of one singular piece of work? Some writers do stick to one particular genre and write stories that include similar elements albeit with different characters and settings, i.e. Tom Clancy who writes military-based novels. Other writers can have a more diverse range and write for different genres, i.e. Jordan Peele who has proven to be successful at writing horror movies but also writes for comedy movies and skits.
Just because DPC wrote one story that featured a very dark plot twist involving a psycho stalker and murder does not necessarily mean they are going to do something this dark again and I honestly feel as though people aren't giving DPC much credit as a writer by assuming they can only do one particular thing. Obviously, they could, but until then I'm withholding judgement and not going to automatically assume that this story will go down a similarly dark path as AL.
Even if we assume DPC isn't going to kill any of the LIs this time (and simply killing one would still be much less extreme than what happened in AL), there are plenty of bad things that could happen. The simplest is that the LIs will eventually each face a major crisis simultaneously, and the MC will only be able to help one of them through it (maybe Maya and Josy as a combo if DPC truly is feeling sorry for AL).
The other girls will survive, but as scarred survivors who never quite get their lives back on track. Maya is forced to live the life her father expected of her. Bella becomes a reclusive old maid. Josy becomes a jaded dancer at the Pink Rose. Jill settles for marrying Tybalt and being effectively a trophy wife. Sage is caught up in Quinn's drug scandal and spends several years in prison. All of those would be far less tonally jarring than AL's finale was, yet would still seriously suck to play through.
That's what I worry about. I like all of the Lis. Hell, I like most of the characters in this game. I want to see them all get happy ending (or learn the error of their ways for the antagonists), and I remain hopeful that is what will happen. But I absolutely don't think we can take that for granted.
Bad things can still happen to certain characters, yes, but I think that the degree to which they will happen will not be as severe as AL.
A good creator knows their audience and even when they are proud with their previous works, they still have to take on the criticism they receive and either acknowledge it or ignore it. AL was a very gritty, grounded, emotionally charged story and I commend them for wanting to raise the standards by writing such a hard-hitting story, but the sharp twist at the end did prove widely controversial and overshadowed everything else. Sometimes you have to read the mood of the room and I'd say that that mood is generally against having this sort of thing, not just in this game, but in adult VNs in general. Even without knowing much about them, I don't see DPC as someone who will dismiss the criticism of AL's dark turn and continue to forge ahead with doing something similar in this game, knowing that people will not like it.
In the Feb Q&A, whilst they did say that they "don't shy away from writing about touchy subjects and feelings", they also said that it's important to "listen to their feedback without taking it personally" with regards to the players and that American Pie was "a source of inspiration together with many other college themed movies". So it would seem to me that, whilst there may be "touchy subjects" in this game, we're not going to see anything too dark or depressing by the end of this. At most, Quinn might go to prison, but then we'll probably flash forward several years in the last episode and find that she's completely reformed and maybe owns a legal weed shop in San Francisco, or something like that. But the LIs, side girls, DIKs, and others will probably all go on to have decent endings and maybe some will have funny, comedic endings like in Animal House.