You... don't frequent those other platforms very often do you? Reddit alone is what prompted this very forum to implement an appeal system after the overwhelming backlash on the poor moderation and just how many people have been banned for dubious reasons at best. Granted, that system is a joke but I digress. The mainsub has complained about numerous things from job design to content itself. Eureka and Blue Mage were particular punching bags. The difference between there and here is when topics start to get out of hand or lose focus, they actually get closed down or removed. With that said, the sheer amount of fanart that tends to dominate led people to make separate subreddits. The Discussion sub is where more well, discussion and debates happen nowadays.
YouTube is filled with complaint or critique videos and Twitch is hardly any different. It simply depends when you tune in. It isn't good content for say, Xeno or MrHappy to constantly bring up criticisms they have towards the game. After all, their primary goal is entertaining an audience. Twitter is probably the only platform you mentioned that does tend to lean very positively, albeit even then there have been moments. It's also Twitter where you're ostracised for "wrongthink". I wouldn't exactly put much stock in what Twitter thinks.
The truth is even people complaining about the game don't hate it. And those generally happy with the game likely still have issues. They simply aren't going to voice them every waking second. I could list off popular YouTubers or Streamers who dislike the job design direction, for example. Reddit has several threads criticizing healer design. There's just not much to really talk about on those subjects. What more can be said about healers that hasn't already?