I don't think they are the worst troop, but they do have the worst build time and their housing and high-cost ratio limit them to be used more. IMO
If Stupercell would only lower the housing and esp the build time (which is think is utterly ridiculous) by half for each.. then they would be one of the better ground troops.. but as current its the time that is the biggest turn off IMO. I think they hold their own otherwise. I don't necessarily mind the cost, but the build time/housing make them inefficient on time, same with pekkas and golems.. you can potentially get more bang for the buck if you can B'loonian effectively IMO.. as it take less time to cook. which is why Barch/BAM are the most popular builds in the game. they are fast and highly efficient on the right base. in the right league.
Like any other troop Valkys need proper support in the right quantities and compositions. (spells included) inefficient yes, but far from useless..

