It looks like at least some version of 0.18.1 is out, and looking at the changelog, the PR that fixed it is indeed there. I can't find the 0.18.1 changelog for the one we're running, but maybe the PR only made it into a later release? https://github.com/LemmyNet/lemmy/releases/tag/0.18.1

(hot rank update batching being the entry in question)

The newest version from Github has this ability!

I'm pretty sure that's not the case. After this long of time, the time decay should have pushed out the older posts by now (I'm seeing almost exclusively 4-5 day old posts on my feed). Using this as reference: https://join-lemmy.org/docs/contributors/07-ranking-algo.html#:~:text=Lemmy%20uses%20the%20same%20Rank,and%20the%20post%20published%20time.

If it really was an issue with Lemmy's algorithm, I think other instances would have that issue too, but visiting them, it's all updated correctly.