You want to find the niche expert subreddits. The ones you named are good. So is /r/badhistory, /r/badeconomics [1] which are generally hangouts of experts to make fun of people claiming things. /r/netsec is generally good, so is /r/machinelearning. Even niche job-specific subreddits (like meddit or /r/protectandserve) are interesting to observe.

Because economics gets politicized so much, it's very rare to find sound discussion in popular forums. It's a ton of people cheering for their "team's" policies.

[1] Full disclosure: I'm recently been made a mod there. /r/badeconomics is probably the highest signal/noise economics place on the internet at the moment though. I learned more there than in school in the years I've spent there.