Oh, now now... breathe in, breath out...
Well, yeah. And thanks for bringing a new perspective on this discussion!
I liken most of these stories to comfort food: the potato chips of writing. And this problem certainly extends to novels, too. Characters are more so self-inserts or based solely on their appearance, sexuality, etc. It feels like dialogue in this instance is fulfilling a program rather than trying to tell a story. But hey, if it's cozy why get out of bed? lol.
Years ago when I worked for a magazine I had to interview an actress about a film she was in. She had the script with her on the table. I'll never forget this, as she spoke to me she put her hand on the script and softly ran her hand over it. I thought, that's how I want to write, I want to write so that someone would hold my work like it was one of their most precious possessions. That's where writing from the soul comes into play. You can use a program to correct your grammar but not to the point where it takes your soul away.
That’s my answer as well. I use ProWritingAid, free version, and treat its corrections as suggestions.
Also, I disagree with all prose feeling the same. I read quite a bit of books every day through club I am in, and I see everything, from ornate prose to deeply layered one to barely understandable chop-mush.
We should all be willing to try out what tools are available to us. Then, of course, pick what we want to use and reject everything else.
This is why I go through and individually choose which things get edited. Grammarly will offer certain suggestions regarding sentence structure and unless I see one I just really like I usually choose to ignore it. Punctuation issues and sentence fragments are primarily what I use it for anyway.
Having written mostly "spoken word" work (plays, audio drama etc.) most of my writing life before starting novels the past couple of years, I'm familiar with the subject of characters sounding alike. This doesn't mean that they should all have different accents or even regional dialects. The best way to learn the difference, really, is to listen to people. I've always been fascinated how different familial groups will speak with each other.
It’s hit and miss. Some stories I look at (and some of them are outside the club) blow me away. Some are hard to read. One I refuse to read because it drove me up the wall... I know that patchy reading is not the best habit, but I am exposed to so many stories each week it helps my writing.
I also have books and writers I simply follow because in some way they grip me. I maintain the Completed&Loved and Read This, Thank Me Later reading lists on Wattpad for outstanding books—in some ways.
Stylistically they are different.
Ants That Carried Us is impossible to mix with MADD Doctor or Wandering God or Renegade (well, Renegade fries my mind tbh) or Seacliff, but they all made it to my top books of the last couple of years.
I do think you have a point about people not knowing how to write how people really talk. It's like the tumblr post about writers not knowing how to write siblings with the "hi bro/ hi sis" stuff. Anyone with siblings knows that talk is weird.
I'm the same way. I prefer writing dialogue that feels organic and real instead of generic voices.
As a comic writer... none of this effects me (beyond spelling that is) XD in fact, comics have different workarounds to grammatical rules.
Not sure if this homogenous writing applies to contemporary traditionally-published YA books, since I haven't read any. But I think another aspect is that a lot of online works come from younger writers who haven't read a large breadth of books from different genres. They simply read other online works and so the "samey" beast feeds itself.
I can definitely attest to this homogenous writing problem. Honestly half the time I turn Grammarly off because I hate their suggestions, especially if I'm doing a dialogue-heavy scene and my characters aren't exactly "proper". I like @therosesword 's idea of writing "like myself", but when I do take inspiration I try to do so in terms of learning how to apply things to my writing. I've always loved the Douglass Adams quote "he flew through the air in much the same way that a brick doesn't", but all that did was make me mindful of just how much strength there is in thinking about how you can paint the picture in your reader's mind. If anything, we should be learning what tools we have at our disposal, not how other people use them.
I agree with you! I personally don't use these writing programs. I know that they can help with grammar and punctuations, but I think they remove that "special touch" your story would have. After all, it's your story, and in my opinion, when you use programs like Grammarly or ProWritingAid to "improve" your chapters, the style of writing you put in your chapters would just... fade away.
Honestly, I think your satisfaction with your chapters is more important than punctuations. If you write chapters without using any writing programs, it kind of makes you feel great, and you would get really motivated as well! (although I don't know if every author feels this way, but I do)
As you can see when you use these programs, the suggestions in Grammarly or any other writing software aren't quite accurate; what I mean by this is... they don't wholly understand your story. If you're focusing on something heavy and emotional on your story, they would still correct your grammar, but they can't help you highlight the impact you really want to bring to your audience. These programs can definitely help you with your grammar, yes that is true, however, they can't help you emphasize your story. They can improve your grammar, punctuation, and sentence structure, but they can't really help you with your novel itself, if you get what I mean.
It's just like what they say, no one knows your story more than yourself.
I use it as a back up check and ignore/double check whatever corrections it wasn't me to make that I don't agree with.
It really hates my fragmented sentences 
Definitely suspect it's a case of writers reading what's popular in their genre and (knowingly or not) emulating it.
I do this too, though I read a lot more physical books than webnovels, and the variety of genres I read has done some kind of odd things to my writing... When I was writing my novel I noticed that it got sillier when I was reading Terry Pratchett, and more descriptive when I was reading Dickens. It still sounded like my voice, but it's hard to deny the influence of what you're reading, even if you're really not trying to emulate.