One thing to remember, though, is that it's the fans that market the game. No marketing department in the world could steer the narrative about Pokémon around the Net to the degree that devoted fans do. Whenever Nintendo drops a new trailer, YouTube is swarming with PokéTubers who analyze it and bring their own opinions. And if kids can find Nintendo's trailer on YouTube, they can (and likely, do) find the PokéTubers as well. Put another way, the kids who don't read Serebii don't watch the official trailers either. Given how much the game hides essential information like how to evolve certain Pokémon, and how this information tends to be aggregated on fan sites, a very large portion of the playerbase will find their way to the fan sites sooner or later.
Likewise, articles about Pokémon on various mainstream gaming sites are usually written by authors in-the-know - they follow the fan sites, 'cause that's the way to get to know the games well enough not to make glaring mistakes. Otherwise, the comment section would quickly call them out for it. Reviews, both professional or aggregate reviews like Metacritic are going to get a lot of fan input. Facebook ads have comments now, guess who posts there? The content that reaches a wider audience is going to be shaped by fans one way or another. The people who play the games but aren't super into them are likely to do a little reading before choosing to buy, and wherever they choose to read, the fan reactions will be there. So when the fans are unhappy, the Internet is going to know. And then consumers are going to know.
If anything, fan outrage makes for a good story for the general news sites. Remember the Fallout 76 canvas bag debacle? It became a pretty huge thing, even though it only directly affected those who had shelled out for a $200 edition of the game. The outrage from those hardcore fans spread far enough to put a pretty big dent in the game's reputation.
So yeah, if they alienate the hardcore fans, it's roughly equivalent to buying a very large marketing campaign against themselves. It's not necessarily that every John or Jane Gamer out there will miss their Abra collection personally, but the perception of lesser quality will spread to them one way or another, and it might influence them to not buy the game, which in turn reduces the interest in merchandise.