I think there is a good difference between the three attacks.
- GK is knife which doesn't pierce thru durability (ex: Dragon Kaido scales in chapter 1002) but on regular humans if hits your insides, your innards are toast. You may mitigate the damage though so Ancient Zoans and ppl like Mingo have a chance.
- Injection shot goes thru durability (like vs Hybird Kaido).
- Anesthesia, since its awakening, circumvents all durability and electrocutes from the inside.
It is more comparable in type to GK, I agree.
I was talking about AP though. Anesthesia, placed on the neck of Meme, got the same amount of blood out (if you excuse the smoke) as IS did to Hybrid Kaido, again on the neck. The benefit is this attack surpasses all durability since thats what Law's awakening brings him.