This sword was upgraded a bit ago to 21/19, I believe. There just isn't an SS for the new ratio.
And you can't really compare SK/Pal 1h weapons to dual-wielder 1h weapons. Sure, the ratio is much, much better on high-end knight 1h weapons, but that's because they lack dual-wield. If you look at two high-end DW weapons (like the acrylia handled broadsword and baton of flame, for example), their damage output would be quite a bit higher than this weapon.