The first example is not redundant, but the second is.
Cunning strike also distracts, removes damage boosts, and reduces crit chance to 0. No other move in the game has this combination of effects, so Procerathomimus still gets use out of it. The DoT effect is redundant for it, but overall the move is not. And of course, as others pointed out, other creatures that are not immune to DoT get full use out of the move.
On the other hand, there is a move that is exactly like fierce strike minus the cleansing of vulnerability: defense shattering strike (and yes, defense shattering moves also remove taunt). Since Secodontosaurus is already immune to vulnerable, they might as well have just given it defense shattering strike instead (which IS still in the game); the “fierceness” does nothing for it. So this move IS redundant compared to the defense shattering version as long as the creature it’s on is immune to vulnerable.