It's not up for debate or interpretation that zfs relies on ram more than most other filesystems. They all use ram, because everything uses ram, and so that much is a baseline that cancels out between anything and anything else.
And zfs uses more and relies on it more than others, above that baseline.
Everything that uses linux pagecache as interface (i.e. everything not ZFS on linux) is way, way more interleaved with memory usage than ZFS, with some extra gotchas due to how pagecache works by mapping disk and memory 1:1 (great simplification, but unless you go out of your way the FS implementation of write()/read() is never used - instead the the same operations as with mmap() are called and write/read calls copy from memory.)
And zfs uses more and relies on it more than others, above that baseline.