You might have some impact across a broad range of people, but the impact that parents have on their kids is far and away greater.

As for shitty parenting, every parent makes mistakes. Not only that, but as kids age, they're also increasingly responsible for their own choices. I'm 100% committed to my daughter, but I'm no saint and I lose my patience with her often enough. If you strive to be better than your parents were, and to do better for your kids, that's honestly enough. I haven't spanked my daughter, and the only time I shout is to catch her attention when she's about to do something harmful.