From the context of the sentence shown in the question above, we can say that Mr. Benton's assistant is a crafty person. That's because a crafty person is a very smart person, but a sneaky, deceitful person who can act controversially to get what he wants. In this case, if Mr. Benton is going to work with this type of person, he must be careful not to be harmed.
Explanation: The weakest to the strongest word would be 'capable, strong then mighty'. Capable connotes to 'being able or efficient' while 'strong' implies the meaning 'ability to produce or withstand powerfully' that makes it stronger than mere 'being capable/able.
