Weight is not the only consideration when you're talking about carrying a folded bike, of course. I don't have experience of all the possible Dahons, but the ones I have seen fold to a much less neat package than the Brompton, which means that you end up carrying it further from your body, which is harder work. Also, if you're carrying your Brompton, you're probably doing it wrong - unfold it and wheel it, or use the easy wheels and wheel it.
Duncan