You stick any current FW (aside from Edgar and Aldo) against LW's like Pettis, Diaz, Miller, and Maynard, and they're gonna get destroyed. And if you want proof LW is better, Frankie is easily better than anybody that Aldo has faced. Seriously, do you think Hominick would earn a title shot at LW if he was the size of a LW?
But at 145 Edgar's size is much more of an advantage, which means he can bully guys a bit easier with his wrestling. Besides that, it's not like Frankie was ever a speed fighter. If he's defined by any characteristics, it's wrestling and technicality. On top of that, Frankie will probably fight at the exact same weight on fight night, and his endurance has been tested, and it passed with flying colors, even after he got beat the heck out of by Maynard in their 1st title fight.