Okay, and Fox still ended the tournament with a positive defensive rating. People just way overthink this stuff. Anyone claiming Fox can't defend against McDavid or whoever and would need to be sheltered and apparently he lost his PP spot to Werenski (through no fault of his own) and that Quinn Hughes coming next year makes him vulnerable are just creating a storyline in their head that sounds nice to them.
Fox's defensive impact against all this big and fast players he supposedly can't defend (something that has been said for years and has literally never proven true in the data) was positive. The issue, if anything, was his offensive impact. He ended the tournament with a positive xG+/-, but with a negative G+/-, which mostly just means he didn't have positive puck in FOUR games. Pretty sure he was on the ice for two goals against and none for. When you look into his usage, he had a lot of time with the bottom of the US roster. The bottom 6 didn't create much offense, and it's not like Hanifin did either. He should've had a better offensive impact, regardless of bad usage, but like I said some of that is bad puck luck.
There's no need for anyone to psychoanalyze the Olympic rosters based on 4 games. You pick your best players. Plenty of the best Americans (Matthews, Hughes, Hellebuyck, etc) weren't that good, yet obviously I would certainly not suggest they shouldn't make the roster. That'd be crazy. You don't get better by picking worse hockey players because your best players weren't at their best in a four game exhibition tournament.