Betrayal at House on the Hill characters: Strength and Weaknesses?
Short answer: They are all balanced in their own way.

Long answer: Each character has strengths and weaknesses, some are harder to spot than others. For example the professor and priest as you pointed out, are mental, but if you look at their stat growth and starting abilities, the priest has more stats that go up to 8, but the professor as more stable stats. It's like this for all the characters. Flash and Ox are both relatively weak mentally, but they each can grow in different directions.

Sorry if this answer doesn't make much sense, honestly this is a difficult question to answer.