From the article: "Large parts of the file API look like this, where behavior varies across filesystems or across different modes of the same filesystem. For example, if we look at mainstream filesystems, appends are atomic, except when using ext3 or ext4 with data=writeback, or ext2 in any mode and directory operations can't be re-ordered w.r.t. any other operations, except on btrfs."

That doesn't mean ext4 is problem-free, but it does mean that other filesystems have different problems that are not fixed by mitigations for ext4's quirks.