Yes Penning needs work on pass-pro but he's a monster run blocker. And you know as well as I do PFF grades it as a won the rep or lost the rep. A pancake hole opening run block is just a won rep. Their grading has its flaws. Plus he is the most improved player on the team , he'll only get better @ pass-pro
They actually get bonus points for pancakes. The scale for every play is from -2 to +2, with 0 being an average rep. A pancake would likely get a +2, which is how he had a few elite run blocking grades throughout the season.