Super Chumps are in a weird spot where it does basically nothing. It's a "displacement" special, but the opponent can affect the displaced area, so you need to be there with your team when the chumps land to do anything with them. But, that's the exact same principle for stuff like Booyah Bomb, Tristrike, stuff that gives solid displacement and is actually threatening. Chump also has an issue where if you follow it up too quickly, you're doing the right thing, but you've pushed the enemy away before the chumps exploded or could do anything threatening, so they get no value. If you're too slow to follow them, they get broken quickly and get no value. Overall it's something of a nothing special, everything it does can be done better with other specials and it's not a salvageable concept. The game already had too many displacement specials so it didn't need to exist to begin with.
Kraken is fine and really cool, literally just nerf clams cheese across the board and the issue is gone. It does have problems with viability, because losing the range on stuff like 96 gal and heavy deco when you pop it kinda sucks, and the endlag means your last few seconds need to be about getting to safety, so it's a special you need to pop at very specific times to make sure you aren't giving up a lot of control by using it, but that tradeoff is interesting imo. It's basically a temporary invincible tetra dualies mode.
Splashdown is just, not good in concept, same way it wasn't in splatoon 2. It can get you killed before it does anything and its aoe, like chumps, can be affected by the opponent. Honestly I think it's worse than Reefslider, and less interesting. Reefslider at least guarantees a dangerous explosion with a large chip radius and has the ability to travel forward. Even if you don't think that, splashdown didn't need to be brought back when reefslider is basically a splashdown rework, leads to overlap.
Screen is really really weak, basically a big 30 damage hitbox, and the only thing it can possibly do to make you respect it is mess with your game's colors and audio, which for some people does nothing, and for some people is jarring and triggering enough to make them unable to play the game.