You can get good answers in /r/askscience sometimes, and the folks over in /r/askacademia can be helpful with career-type questions.

In general though I find most of those other subs to be pretty disappointing. I know the mods over there do their best, but /r/asksocialscience is a disaster zone.

It's hard. Reddit is not really a forum that's conducive to what these subs are actually trying to do (give people accurate, expert answers). Heck, for all the praise that this sub gets, and for all the work the askhistorians mods do, this sub just barely manages to keep the tone/quality of discussion high enough for me to want to post & participate. That's a credit to the mods here, but it also speaks to how fundamentally incompatible reddit is with the kind of discussion which everyone hopes to find in these subs.

I'm biased, but /r/linguistics is quite good for (surprise!) linguistics-related questions, including those on linguistic history. A lot of the people giving answers there either have graduate degrees in what they're answering on or they're in the process of getting them. The mods also make an effort to remove guesswork and speculation much like what happens here, though not quite as strict. There are other places to ask linguistics questions, but /r/linguistics really is the best place for in-depth answers from people who really know their fields.

Then again a lot of those people giving great answers there also subscribe and comment in AskHistorians, so it's not always necessary.

Unfortunately, I feel like a number of the academic subs haven't quite sorted out the signal-to-noise ratios, so it's still pretty easy in some subs to get terrible answers that are highly upvoted, while the guy who really knows gets buried. This happens more than I'd like to see on /r/AskScience, for example.