DS9 had its share of darkness. Picard’s torture by the Cardassians is unforgettable. But B5 “darkness” went on longer IMO, than some of the story arcs in DS9. The tragedy of Londo Mollari. The tragedy of G’Kar. B5 “lightness” sometimes came from the occasional one step back, for every two steps down.
But I’m really looking forward to the DS9 documentary; it will give a taste of what a full DS9 HD transfer would look like, if CBS could be convinced to spend the millions necessary to create all-new HD effects. (Detailed article.)
The same video effects upscale / remaster problem applies to B5, but it may be possible some day (with caveats).