There is more to it than just dwell. 340 dual points had a ball bearing breaker plate, and dual points last longer to some extent because each set only works half the time, so to say
Also, SOME dual points, like the old Prestolite hemi/ RB tach drive units, also had a ball bearing upper shaft bearing.
Also is point float is an issue in a single point, it is mitigated by a dual point, usually, given the same points are used.
