But the point of the set is not because Swift Swim is better, and Corviknight doesn't need Attack EVs to be good. I can't stress enough that it OHKOs or 2HKOs loads of Pokemon that are specially defensive in its tier without the Life Orb (I forgot to use it in the calculations)
252+ SpA Life Orb Cramorant Surf vs. 252 HP / 88 SpD Corviknight in Heavy Rain: 243-289 (60.7 - 72.2%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Life Orb Cramorant Hurricane vs. 0 HP / 0 SpD Scrafty: 343-406 (126.5 - 149.8%) -- guaranteed OHKO
252+ SpA Life Orb Cramorant Surf vs. 248 HP / 252+ SpD Shuckle in Heavy Rain: 187-221 (76.9 - 90.9%) -- guaranteed 2HKO
252+ SpA Life Orb Cramorant Surf vs. 252 HP / 252+ SpD Carbink in Heavy Rain: 257-304 (84.5 - 100%) -- 6.3% chance to OHKO (Or a guaranteed 2HKO)
252+ SpA Life Orb Cramorant Surf vs. 252 HP / 4 SpD Cursola in Heavy Rain: 188-224 (58 - 69.1%) -- guaranteed 2HKO
Why is this downvoted? Even if Agility is "Wasting a move slot", Defoggers can get rid of SR for you. Setting up isn't the worst possible thing to happen. You've seen the damage output Cramorant can give multiple times, and it isn't uncommon or looked down upon to set up, Bulk Up Corviknight was just mentioned and Swords Dance, Dragon Dance, and Nasty Plot are all commonly used. Honestly, I think "cheap" is a bit harsh, just because Swift Swim users exist and are good, doesn't mean that there are no other Rain Sweepers.
That's my opinion anyway, and even if you disagree I don't think this moveset should be downvoted.