Have you ever actually watched Devin Harris play defense? Considering the way Chris Paul curbstomps him every time they match up, I'm shocked you'd say Harris is "especially" better at defense than Kidd.
Harris doesn't play defense so much as he goes for charges and flops his ass off. I'd say Harris plays Tony Parker & Rajon Rondo much better than Kidd, but Harris' Charmin-soft defense against Baron Davis & Dwyane Wade ed over the Mavs big time. I'd even go so far as to say that if you replace Devin Harris with Jason Kidd in the 07 playoffs, the Mavs beat the Warriors in 5. I'll take Kidd's savvy play on D over Harris' fishing for calls any day.
Are Devin's feet quicker than Kidd's? Absolutely. Overall is he better at defense? ing no.