Not to put this thread to far off topic, but the idea that Viaduct is a bad map because of abusable sniper positions seems a bit off to me.
To be clear, Viaduct sees play in every competitive format. Sniper play definitely occurs (for the reasons cited above) but it is by no means completely disruptive, and managing to deal with the sniper is a bit of a skill tester IMO. Obviously, competitive play doesn't have to be the end all of decision making when it comes to what makes a good/bad map, but when a very dedicated group of extremely talented players (many of whom play sniper exceedingly well) have learned to adjust to a specific sight-line issue, I don't think it makes much sense to question it (or at least, not very much).
While the idea of "don't promote sniper play, good snipers will find their own spots" sounds nice in theory, in actuality its way to much of a limitation to really be taken seriously when designing a map. Its a kind of "in an ideal world in which all maps were perfect and every class was balanced relative to one another" sort of theory that really doesn't account for the actual reality of how TF2 plays and how specific maps actually work.
And the idea that koth_king is a superior map because of the way it shuts down sniper sightlines seems like the sort of idealized, armchair map theory that doesn't really result in producing maps that people actually want to play.
Just my 2 cents, I think that screenshot looks fine.