Off topic: This seems to be an odd emphasis on the word "good". Can a native English speaker confirm?
I agree that use of "good" is questionable here. One would think that without the skills mentioned, one wouldn't be a theoretical physicist at all . (Is every person who lacks these skills a "bad theoretical physicist"? Only in a vacuous sense.) That said, I think we should interpret "how to become a good theoretical physicist" as "how to gain the competencies that are expected of s theoretical physicist."
A bad theoretical physicist is one who only understands enough to sound smart to their friends. AKA, a crank.