Must be said that I've seen the "I am a hard worker" line used to good effect, the trick is to be believed. Like every other claim you make at interview and in your CV, you should have at least one example of it in your life.
Achievement is a function of sweat and brains, and on paper it can be hard to separate the two.
Quants tend to be drawn from the smarter end of the distribution, and some smart people cruise along, which is fine until they hit some swamp that just requires a hard slog to escape. Some managers have had bad experienced with staff like this.
So it's not the worst line you could use, maybe not the best either, but above all the line must be true.
The optimum answer of course is highly tailored to what you've learned about the role through the interview and by your headhunter digging. You need to discover what is important to them and say "I've learned that X is important to the team's success, and since I'd done a lot of Y, I think I can make a good contribution".
The optimal Y in this expression is not just maximising it's utility with respect to achieving X, but also finding a Y that few other people have.
An issue with any MFE/CQF is that you are learning stuff that quite literally thousands of others are being taught, and most of them aren't dumb or lazy.
Thus to well answer the question "why should we hire you not another ?", you need to start work now on a few Y things that your peers aren't doing. That Y should be something you can excel at, and enjoy. Even if you pick a Y that you feel works in many jobs, be prepared for it not to work in any given interview. This strategy gives you an extra shot that your competitors may not have, and in a highly competitive game the expectation of this is good, even if the distribution of outcomes is wide and includes a lot of zeroes.
