Lol. Minecraft alone proves you wrong. 4chan is where Notch first posted early builds and got feedback.
No argument on it being a cesspool. It is, and has been, for a long long time. But plenty of good stuff happens there too.
/vr/ has unearthed a large amount of formerly lost media (guides, promotional material, entire games! Most of Osamu Sato’s work outside of LSD Dream Emulator had effectively been lost before they got onto it) and is often the spot that leaked stuff drops, like the huge Nintendo leaks a few years ago. The Doom threads there have had a hand in some big, well known mods. It’s arguable that Sonic Robo Blast 2 Kart grew out of those threads’ failed Doom Kart project.
/g/s “friendly windows thread” is decidedly unfriendly, but the guides and links in the OP are wonderful resources on how to set up and configure new Windows installs. I haven’t seen the info there laid out as well and as easily digestible anywhere else.
/vg/ has a large number of threads that are really the only source for certain info about certain game series. The emulation general threads are great resources, and the wiki built from them is the best go to one stop shop for info on emulators. The amateur game dev general threads have been the building grounds for a decent amount of games you’ve heard of before. Risk of Rain is a good example. Hopoo started his game dev journey in those threads. Any game that references “AGDG” is shouting those threads out.