Likely he doesn't want you to turn into a potioneer who brews like Black, perish the thought. Not that I can picture you ever giving up pride of ethic and process in favour of expediency.

I've read of regressions but Slughorn doesn't have us do them. I think it might be covered in the seventh year NEWT lessons, but even then only as an optional study. Which means that you're already well ahead of me and everyone else in Potions. Well done, brilliant one. Are you entirely sure you're a Gryffindor?

Oh, wait, you gave your one and only portkey to the Longbottoms and Luna out of a noble sense of right and wrong? Never mind then, you are a Gryffindor. Just an exceptionally non-expedient one.