My Obi Wan is maybe 10-15% brighter than my Anakin. I bought them about a month apart from each other, so they are both late models.
Most people do report the Obi is the brightest saber, but twice as bright would be a lot. I'd guess that means either you have the best Obi on the planet, or an older Ani, or maybe the batteries in the Ani aren't as good.