Van Ness' issues coming into the draft were that he lacked experience and development, especially at the edge rushing position as he was basically a college pass rushing DT and then spent about half of his final year as an edge rushers but was still rotating in at DT.
Also that he only had one pass rush move down, the bull rush. Now he was absolutely freaking great at the bullrush and if you're only going to have one move, then it should be the bull rush, as it sets up other moves the best, BUT at the NFL level, if the only guy knows it's going to be a bull rush every time, then they can prepare for it and do pretty well at it.
So basically Van Ness, needs more experience, development and to expand his pass rush move set, but I think all the physical skills are there to work with.
Also, I know some hated how LeFleur basically ripped a reporters head off for not knowing football when he was suggesting the 3-4 OLBers, aren't 4-3 DE, but I totally agree with LeFleur, that reporter was trying to tell him what to do, and the Packers 3-4 OLBers were absolutely huge for OLB and they do have 4-3 DE size, and basically are the same exact role, position, despite the label change.
The smallest edge rushers that the Packers had consistently seeing the field was Kingsley Enagbare, whom has lost some weight and now about 6'4" 260lbs, and Enagbare's weakness was limited athletic upside potential, but he was extremely physically and tough and could probably put on weight and play DT. So you can't tell me he wouldn't fit at 4-3 DE as well since he was currently playing 3-4 OLB.
The next smallest of the guys seeing the field is Preston Smith, at 6'5", 265lbs. Now Smith might lack the perfected pure power you want, but he more than makes up for that with freaking long arms, knowing how to use them extremely well to get leverage and containment. And Preston Smith has played multiple years as a 4-3 DE while in Washington... so you can't tell me he can't play 4-3 DE at the NFL level.
Some of the backups might be a bit smaller, but they haven't been seeing the field much.