Punchshroom
FISHIOUS REND MEGA SHARPEDO
Carracosta's speed is what sets it apart from most other setup sweepers, and it's not a good thing either. This limits how much Carracosta can switch out to set up again later in the game (basically almost no chance). Carracosta also has a quirky speed tier: it's fast enough to outspeed a good portion after +2 with maximum speed, but sacrifices notable bulk as a result, not to mention its setup move further reduces its bulk. That combined with the lack of initial speed means Costa will have to take 2 hits against faster opponents, which will matter even if their attacks don't hurt that much at first (ex: I can't switch Costa into unboosted Samurott's Waterfall, which 3HKOes, without taking yet another before Costa can even move; if I bring in Costa on a double switch/KO, Costa can take the Waterfall well enough to Smash, but its -1 Defense leaves it more vulnerable to Aqua Jet). These traits combined limit the amount of opponents Costa can setup on, as even a poke with only 100 base Attack and 80 base power STAB is still not considered easy setup fodder despite what Costa's great defense would imply.
And then there's the part you missed where I'm no longer arguing for Carracosta going to A-Rank, good day sir.
And then there's the part you missed where I'm no longer arguing for Carracosta going to A-Rank, good day sir.