As OP was rightly pointing out, there is a discrepancy here between output and size.
LinkedIn for example has many of the same issues and a lot more complex functionality. They manage to do this, compete with Indeed (and have a higher market share), with a relatively small number more people.
Or are you saying LinkedIn has 14,000 employees just for their job board functionality, and only 6k for the other larger, more complex parts of their system?
No? So what explains the relatively small percentage difference in employees but a large difference in functionality and market share?
Job board popularity varies greatly by country, but from the look of it LinkedIn has more of the global market share of Indeed.
My point is that unlike indeed they do this without jobs being the core, 100% thing they are dedicated to. Even if they are slightly behind in market share the point still stands that LinkedIn is clearly doing more with less.