I agree, and I think the issue extends beyond just First Posts, to a few aspects of community moderation.
There are certainly enough users to handle the queues, if even a small fraction were consistently active in the review queues:
249 users who can access the review queues (>= 500 reputation)
28 users with close vote privileges (>= 3,000 reputation)
Bearing in mind that only one user is needed to review a First Post, and we only get at most 10–20 questions/day, there are, in theory, sufficient users to handle the flow of questions.
Unfortunately, we can't expect every user with sufficient rep to be here every day. I suspect many of these users haven't been active in months, and far fewer actually visit the site on a day-to-day basis. Even fewer actively contribute to review.
Many review tasks spread across few reviewers leads to the situation we have now, where dedicated users like you have to handle an awful lot by yourself (thank you for doing that, by the way!). So many systems rely on review working, and we need more people to share the load. I've been trying to contribute what I can personally, but the queue always seems full!
The same seems to be the case for the Close Votes queue (and question closure in general) — it's rare to see a question closed without a binding vote involved, which is unfortunate. Generally, moderators only use their binding votes on blatantly inappropriate posts, and that's a good thing, because ideally users should be able to decide what to close democratically.
In reality, there are probably less than 10 users who actively are able to close questions, which makes it much harder to close questions in a timely fashion and give the authors feedback on how to improve their question.
So what can we do?
Ideally, we need more reviewers, and to figure out why people don't review. Is it simply because we need more users here? Are the users here who can review choosing not to? Can we incentivise reviewing?
I don't feel like loading more reviews on to the users who are doing this already is sustainable. Honestly, reviewing 20 posts a day, every day, just to keep the queue down, stops being fun. The only real solution here is to spread the work across more users, or else the site's bus factor drops dangerously low.
Encouraging people to review is hard, and encouraging people to review well is harder. But a thread like this is a start. Raising attention to the problem is probably the best solution for now, and the new top bar might affect reviewers anyway, so it's worth monitoring.