There's proof that it CAN be done, but it's overwhelmingly hard to do. Again, it's easy to say 4 of 10 with no context, but like I said before 2 of those guys are HOFers drafted 20 years ago. And one is Nick Foles who got on a hot streak and is now a backup like he's been 90% of his career.
The narrative is being carried by Russell Wilson. Wilson is the only example of the last 15 of a great QB drafted after the 1st. Sure guys like Cousins, Jimmy G, and a few others are solid-to-good starters, but the elite guys are typically the first rounders.