Your wrong in this basic. So the rest of your argument falls with this presumtion as it is based on this being true.
For example the good old Rapier/Scimitar is best when you have significant sneak attacks (lets define this as 7+ levels of Rogue) and thus can reap great profit with a Radiance Rapier/Scimitar from the much higher crit range.
Or the Rapier/Shortsword combo on a Drow/Elf who doesnt have bonus feats in abundance (so every non-Fighter character), who has an effective +4 to hit over the dual-Kopesh guy. +2 from racial enhancements, and +2 from being able to spend the feat on OTWF instead of EWP:Kopesh.