I like that. It does seem like Harry's dark side is the one that can find a win in any situation, and that does seem to be his strongest power - just the will to win, and the means to calculate that win.

But there is also:

For once, just once, Harry hadn't gotten shortchanged in the mysterious powers department.

After almost a month of work, and more on a whim than any real hunch, Harry had decided to make himself coldly angry and then try the book's Occlumency exercises again. At that point he'd mostly given up hope on that sort of thing, but it had still seemed worth a quick try -

He'd run through all the book's hardest exercises in two hours, and the next day he'd gone and told
Professor Quirrell he was ready.

His dark side, it had turned out, was very, very good at pretending to be other people.