Dagors have a focus shift due to zonal spherical abberation. This gives the "sharp but smooth" look of a wide open Dagor that some like, especially for portraits. The additional design freedom of the Plasmat allows designers to eliminate that focus shift, which is why Plasmats became popular after coatings came in. Wide open Plasmats tend to look a bit harsh due to the lack of aberrations, but that's the price of getting rid of the abberations/focus shift.
Some may prefer the look of a wide-open Dagor while others prefer the look of a wide-open Plasmat, and some may like this for this but that for that... Stopped down, Dagors and Plasmats look pretty much the same, with the Plasmat having slightly less coverage due in part to the slightly longer barrel owing to the additional air spaces.
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