Can I create posts on behalf of another user via REST?

One caveat for larger communities: keep an eye on the indexes. At a few thousand rows the difference is night and day.

Great point. I had not considered the angle you raised in the second paragraph — it reframes the whole thing for me.

Could you say more about how you measured the result? I want to try this but I am not sure what success would look like.

I respectfully disagree on one detail. In my setup the opposite held true, though I suspect it comes down to community size.