I'll have to be honest, I think you're right in saying that MC threads' quality has declined in the past few months, heck I'd say starting from 2017, going back to GAF's last months. I feel that these threads have gotten way too much focused on people trying to "GOTCHA!" each other, without enough meaningful conversations. Basically, a fight between extremistic positions due to one side starting hyperbolising facts and feelings and the other reacting accordingly because they felt the NEED to do that, thus leading to the current situation where it's far from unusual to see users not being capable enough of having conversations, even if based on facts. I feel that the current situation, while not (usually) reaching the peaks from past MC threads, is worse due to how constant this behaviour is. Is it due to Nintendo now doing very well, thus bringing more fans "uproaring" about their success, even "aggressively" as a reaction to years and years where some Sony fans mocked at them? Is it due to several people, as duckroll mentioned, insisting so many times that Japan doesn't matter, the West/Asia/Mars will save whatever game starts underperforming in Japan...right in the thread about Japanese sales? Is it due to the forum expanding, however by attracting more "similarly-minded" people, thus mostly resulting in the noise getting louder and louder, with conversations being less and less of a factor? It's probably a combination of several elements, potentially not just in Media Create threads, but I feel something should be done about it.
I'll certainly try to participate more in these threads, with facts / numbers / I hope good starting points of conversations, and hopefully other people will follow. Better MC threads mean more people who can be interested in joining them, a better environment overall. I hope things get better, it just sucks to see the threads going like this nowadays.
Sorry for the excessive answer, but it's something I wanted to express for a while.