I completely disagree. Mechanics matter.
Powerful Charge is a wash, since its just a damage boost, but in cases where a feat buffs the attack roll, believe me, it matters. A player is going to have a tough time RP-ing her "Death Dealer" fighter if she needs a 15+ to hit. "Die, and return to the Hell from whence you came!" <rolls an 11> "Damn, missed again."
Simply put: You can't RP being good at certain things in the game if the numbers don't add up.
But how you get those numbers to add up doesn't matter. If you want to be known as a "death dealer" and feel like you need to have a certain attack bonus to accomplish it... then you can do so in many different ways. And whether you see the word 'Expertise' in your feat list matters not.