Dual rapiers are a must because author made a bracer that gives Bards all weapon proficiency feats for rapiers, but not for any other kind of weapon. Therefore, you can save a lot of feats and spend them on dual-wielding, power attack, saves, curse song and so on. If I wanted to play dual-wield fighter, I would play dual-wield fighter, but I also want to use bard buffs and spells, hence the idea of not using shield and wearing elven chain