Both of those subreddits are actually pretty poor mediums for "serious" discussion about quantitative finance. There's been an uptick in cryptocurrencies on each lately, and the subreddits are mostly saturated with early-career, "rate my algo" and "how do I mean reversion" questions from beginners.
For obvious reasons, there really isn't anything great out there for non-beginner stuff. http://www.nuclearphynance.com/default.aspx is probably the best out there but not very active. Very deep archives though.
https://www.reddit.com/r/quant/
I'm exaggerating, but only slightly.
https://quant.stackexchange.com/
https://stats.stackexchange.com/
The NYC FinTech Meetup is also usually a good place to network:
https://www.meetup.com/NY-FinTech/