Literally why is anyone surprised about Serebii being a shill? It's literally his livelihood, why would you expect him to say anything bad about the thing that feeds him?
If you don't like his conduct, let this be a lesson for the 95% of you here who are underage to stay in school and build actual careers. If Pokemon disappears what's Joe going to do? He can't move on to a new franchise, his personal brand is too tied to Pokemon. What's he going to get hired as?
serebii.net is basically a site from two decades ago so it sure is fuck isn't anything related to the technical aspect of websites. Is he good at engaging consumers? You already know the answer to that.
For a fun little thought experiment, imagine you're Joe from around the beginning of Gen 4, late 2006. Diamond and Pearl have released in Japanese. The internet is taking off, and more and more people visit your site every day for info on the latest Pokemon games. You may very well have a shot of doing your dream job, making money by operating a Pokemon fansite. But how do you do that and not end up in this limbo of being inexorably tied to the brand while not actually being a part of it at Nintendo? What if Pokemon fades away? How do you hedge your bets?