In Chess, Rooks are more valuable and powerful than Bishops and Knights. Why are they little nubbins in this game? Those guys ought to be Pawns, especially since their attacks are rather one-note. And if we're going by size between Knights, Bishops, and (dilapidated) Kings, then actual Rooks ought to be house-sized.
Also, the angular worker drones ought to just be Serfs considering they're purely noncombat. Plus it fits in with the feudal theme.
Valuable in terms of a higher point value in conventional scoring sure, but ultimately saying they are more "powerful" than a Bishop or Knight... That depends entirely on playstyle and positioning.
Speaking of positioning, consider the starting positioning of the pieces on the board. Pawns at the front, as is their lot, the King and Queen at center with the Bishops and Knights closer to them then the Rooks.
More valuable...? Debatable.