Alexi covered it well. I'd just like to add that Rance is also ignoring the fact that at the end of that not-so-potent Fast Blade + Savage Blade in FoF, you've set yourself up for a high potency RA that you can use immediately after. Once you factor in that next GCD:
With Fracture: FoF(Fracture+Fracture)+Fast Blade --> 1.3x440=572 + 150 = 722 total potency for 2 FoF Fractures plus step 1 of a new RA combo.
Without fracture: FoF(Fast Blade+Savage Blade)+RA --> 1.3x350=455 + 340 = 795 total potency for FoF Fast and Savage blades and finishing with RA out of FoF.

Fracture just isn't worth using as a PLD at 60.