What you say makes lots of sense. I can see how hit rates not being passed down would cause issues.

But anecdotally I think I'm in the same spot many others are. Btrfs let me down a couple times (once lots of truncated files and another time I ran out of inode space on a mostly empty disk iirc) and I'm in no hurry to give it another chance.

zfs has just happily worked for me. I ran it as a root filesystem for years. All the snapshot/send/receive stuff just worked and stayed out of my way.

Note that this was for personal use and with SSDs and later nvme so I wasn't comparing it head to head with anything. Which might be why I didn't notice issues like page caching behavior.