I think Z has addressed this very well with her response, but I just wanted to specifically address this bit here:
I can’t speak for anyone else on the team, I’m part time and on a different type of contract to most of the team, but the KPIs laid out in my contract are more abstract and don’t involve a particular product/feature. They’re related to the engagement of the community as a whole.
If there is sufficient evidence that the accuracy (and/or promptness of fixing inaccuracies and issues) in the Daily Challenge questions has a direct large impact on community engagement and retention, then it’s an obvious business move to put more resources into it. As of now, though, there are other (measurably important) factors at play, many of which aren’t publicly visible. Some of them may become visible in the future, many will not, though. 
I personally love the Daily Challenge, and it’s one of the things that kept me coming back to the community every morning (and still has me coming back daily on my civilian account at my other job) but part of the charm for me has always been that it’s community members’ submitted questions. To me, it’s always felt like another way we could share knowledge with each other, but due to the Dunning-Kruger confidence curve, one of the times you’re most willing to share knowledge with people is when you may not actually understand it yourself, so sometimes we get things wrong.
As for reviewing and fixing the questions, one of the things I’ve been trying to do is to keep newer questions under control, as we had a situation where we’d run out of new questions for certain (consistently active) community members to take, so I’ve been giving the newer questions a higher priority so our most active members can continue to enjoy the feature. I’ve also been trying to prioritize questions with the highest number of reports. Unfortunately for this one in particular, it doesn’t look like I can see the number of reports anymore, presumably because it’s been placed into moderation, but the more reports, the higher priority I give them. Unfortunately, there are quite a few folks who will voice their complaints in the comments of a question but not flag it for review, so I don’t always have accurate numbers to work on there.
I also wanted to address these (mostly because I myself also like seeing stats, and I hadn’t actually gathered them on the reports yet)
[ How many questions in the flagged queue? ] There are currently 484 questions with “unreviewed” flags on them, meaning no action has been taken yet. The mass majority of these only have a single flag (>200 of them) and are very low on my priority list at the moment. (don’t worry, I didn’t count them manually, I basically used a “find/replace” tool to count them for me😁)
[ How many people looking at them? ] I believe I’m the primary reviewer of these reports at the moment, I know I’ve seen @david-k-spiceworks helping out with questions at least a few times (thanks David!)
[ How many can each person address per day? ] As Z mentioned, this isn’t currently a constant. My contract states a maximum number of hours I can work per week, but my time is primarily limited by factors outside of SWZD’s control, and I don’t think I’ve ever been able to dedicate even close to that maximum. Feel free to blame me for that if it makes you feel better 
Even if I did have dedicated time, though, the amount of time each takes greatly varies depending on the quality of the original question, the source provided (if one was provided), my existing knowledge on the subject, the quality of the information in the reports themselves (some just say “this is wrong” with no context as to why, for example), and the community’s response to my suggested edits, as I’ll often ask the community (or at least authors) their thoughts if I’m not particularly confident in my knowledge of the subject, or if it changes the question significantly from the original.
I hope this helps!