You have raised some very good questions, which in my view are arguable for different views.
"Is the ability to ace interviews a prerequisite to be a good consultant ?"
>> Personally, I don't think it is, as I've seen so many really bright and hard working people failing in the interviews and then making into other jobs similar to consulting (e.g., internal strategy department) and becoming amazing "consultants". However, the issue is that if you're not able to ace the interviews, your chances to get into consulting are very limited
"but is being a great interviewee mean you will be a great consultant ?"
>> No, there isn't a single consulting firm in the world that can say its interview method is 100% accurate and establish the relation you imply in your question; however, the large large large majority of people that ace the interview will indeed become a great (at McKinsey we often have a joke about 5% of new hires being a casting error.. but the real number is actually much lower than it!)
Great input as always.