Hendricks being the 9th overall pick after having a composite HS rank of 67th (according to 247, who had him ranked 84th) is incredibly rare for a one and done player.
If you aren't in the top 50 of your class, it's pretty rare for you to be one and done, much less a lottery pick.
You're really nitpicking if you're pushing back on Hendricks being an unknown prospect in draft circles prior to the season starting. He might have been a footnote in the biggest draft junkies pre-season outlooks.
The only other guy who comes to my mind in recent years was Josh Primo, who had a huge range among the scouting services, (247 had him in the 20's while others had him in the 80s or not even in the top 100) and we saw how that turned out (even before the weird **** he was not looking good).