Interesting that this comes up, because this design philosophy is what I disliked about the weapons in the Kalamar Player's Guide, as well.
Why? I think it's important that you have a lot of flavor in your game, and that you try to have a role-playing intensive campaign (you know what I mean). The problem with that aren't the players who like, or love, flavorful characters. These guys make even boring choices interesting because they add their own flavor.
No, the problem is with those guys and gals who prefer a more simplistic approach (I use problem strictly in the sense of getting a flavorful game going, because otherwise there is no problem with such a preference). You have to show these players that flavorful choices can be just as cool as their mechanically influenced ones, if not cooler. And you're not going to get there by making all flavorful weapons (like the leafblade et al) mechanically unsound choices.
That only leads to having "min/maxer" deride "flavor-friends" for being inherently weaker.
In short, if you make flavorful choices mechanically unattractive, you're not going to get more people choosing them, but less. And I don't think that's what you want, any more than I do.