Shanks one shotted Kid, Blackbeard defeated Law after taking some damage. I’ve seen a lot of people claiming that this means that Shanks>Blackbeard or that Law>Kid.
However the way I understand it, it’s less about the difference in strenght between these characters and more about their personality and circumstances. I think what Oda intended was to show us that Shanks tries to finish his fights in a fast and efficient way without fooling around, especially when his allies are in danger.
Meanwhile Teach is someone who likes to play with his oponents, not going all out from the start. This is why Kid got clapped hard while Law put up a fight. Blackbeard’s face is covered with blood because of the first attack but seems like nothing else happened to him. “Soundly defeated” means everything.
I believe Blackbeard is more or less equal to Shanks, while Kid is more or less equal to Law, and if they switched their opponents then Law would get clapped while Kid would land some good hits on Blackbeard. However, neither of them can be considered Emperor level.