You're making the claim ;) The main thing an fs is, is a layout for data on disk after all, no mainline fs will do this in a way that is particularly consumptiv

You're making the claim ;) The main thing an fs is, is a layout for data on disk after all, no mainline fs will do this in a way that is particularly consumptive of resources. Specific features like RAID and deduplication are known to add to RAM and CPU requirements. Synology uses BTRFS for neither, so any performance differences are almost certainly not due to the specific fs. I also have not seen any evidence of perf diffs.