Where, exactly, is the challenge in following written and extremely detailed instructions as closely as possible? Sure, you may forget about steps or do something not entirely the right way, but it's kind of hard to see how there's much room for being good or bad at the subject. Surely real talent is only displayed in coming up with new Potions, or making modifications to existing recipes, the way the "Half-Blood Prince" does but apparently nobody else. That they didn't do that sort of thing in early years is understandable, but these are NEWT classes - if they don't learn it now, when will they?

Then again, I suppose in a way that's not very different from high school classes in most subjects in the real world, which are also mostly about reproduction. But those at least don't have detailed instructions for everything, and make students think for themselves about how to solve problems or questions.