Slashing Grace
Prerequisite(s): Dex 13, Weapon Finesse, Weapon Focus with chosen weapon.
Benefit: Choose one kind of one-handed slashing weapon (such as the longsword). When wielding your chosen weapon one-handed, you can treat it as a one-handed piercing melee weapon for all feats and class abilities that require such a weapon (such as a swashbuckler's or a duelist's precise strike) and you can add your Dexterity modifier instead of your Strength modifier to that weapon's damage. The weapon must be one appropriate for your size.
The description is fine as is, considering "weapon finesse" requires a "light weapon, elven curve blade, rapier, whip, or spiked chain...", this seems like a very odd feat.
Unless you SPECIFICALLY only use this feat for a slashing light weapon or the curve blade you either get to use weapon finesse, or slashing grace exclusively.
For example:
Longsword uses STR for hit, but DEX for damage
OR
Rapier uses DEX for hit, but doesn't qualify for the feat because it's already piercing (wha...?)
It just seems very counter-intuitive to me.