When Sherlock tests for the force to detach the jeweler's wrist, he uses a Gun Tackle assembly and states the load registered on the balance gauge is 495 lb.. That load is one-half the resistance at the pin connection (wrist), so he should have stated the load necessary for the wrist to fail was 990 lb.. Assuming. though, the 495 lb. is an accurate number in reality to detach the wrist (corroborated by a medical professional in the episode), the force which Sherlock needs to apply to detach the wrist would be 247.5 lb., i.e., what the balance gauge would read. As he is merely standing and pulling down on the rope, Sherlock should have known he still could not do this using only his body weight in the system and that he would need at least a Luff Tackle assembly (165 lb.) to complete his test (or used another floor connection and pulled up on the Gun Tackle assembly.)
It makes no sense for the criminal mastermind to try and find a criminal weightlifter for the hit on Shapiro specifically so he can pull the handcuffed case off Shapiro's wrist with his bare hands. Any kind of minion would do. They could simply bring some tools to separate the case in any number of ways.