I actually stomped the Duo first time round due to having summons and Rikard's ludicrous sword. As an old hand at Dark Souls I decided it would be "fun" to experience the most kick-in-the-nuts version of the fight possible, which makes Ornstein & Smaugh seem comparatively fair (tbf I also stomped them first time before learning how the other builds lived). In the end I was still quite underlevelled but at least had optimised to dual bleed twinblades, as two-handing just wasn't cutting it.