With Billions of people around the world, one can only expect and accept that not everyone will like the came. Hell, I've had plenty of people tell me that a story I wrote isn't their cup of tea, but that doesn't mean it's bad. I doubt this is criticism since someone who brings criticism up usually is to help a creator improve, not belittle or throw accusations out the window. I have my own thoughts of Reborn and I can even understand that post you linked in the OP. There's just a bunch of terms thrown around that have become so general or broad that they mean so little. Edgy is one such term.
Is Reborn edgy? In the olden days, the answer would probably be no, but the term has become so broad that it's yes. I mean it could almost be applied anything that uses dark elements which is basically almost any story. Over the years, a lot of writers' writing grows darker since they try to be more realistic since not everything is lollipops and dandelions. Not everyone likes dark stories but you'd be surprised by the number of people who like dark elements in plots since it brings suspense and usually a few wow moments. So basically, using the word edgy is so confusing that nobody can really understand what you're saying.
Now back to Reborn's design, you can see quite a bit of Colosseum in Reborn City if you compare both games. Tbh, the actual city is not that much darker than Colosseum. The biggest difference is that there are mutated Pokemon rampaging Reborn City. So you're almost arguing that a children's game is "edgy" and way too dark. Reborn is certainly not a children's game as it goes into more mature themes like sexuality, depression, suicide, etc. Most of that was based on the league since characters played those roles and some were actually real. You wouldn't remove Lincoln's assassination from a game just because it's too dark. It's an event and should be included.
The tumblr fanfiction statement is also kind of interesting. That's just horrible slang for amateur writing which Reborn proves itself at points it can be quite mature and make good use of vocabulary. There's a lot of different characters who all try to speak differently since rarely does everyone use the same dialect as that'd get very boring, and very old quickly. The writer's knew what they were doing despite such tight constraints. 34 pre defined characters is easier said then done to work with. Besides, this is Pokemon. Since when are you expecting a Stephen King novel in a series known for cookie cutter plots.
Tbh, you I can't take serious but the person you linked I can take quite a bit more. Instead of bashing on the game, he gave his reasons for not liking it. It's okay to have an opinion since nothing is perfect. I'll save my own opinions for when the game is complete, but I don't think Reborn as the best game ever (it does everything I want from a Pokemon game though). If you were willing to act a bit more mature, I'd gladly talk about the cons of Reborn, but there's no point as of now.