HN feels mid-size in a good way. Most forums are a lot smaller, and then there are the few famous ones that are much much larger. There aren't that many in HN's order of magnitude. The mid range is a nice place to hang because although the problems are impossible, they're not utterly impossible. You can work with them around the margins.
The most interesting number is the 1300 submissions because that hasn't grown since 2011 - it just fluctuates. Everything else has been growing more or less linearly for a long time, which is how we like it.